PHYSIOLOGY 


.117      1-41  1)\/'T  A  TV 


R.  ANDREW  W';LSON,  F.R.S.E 


-NRLF 


BIOLOGY 


Human  Physiology 


PHYSIOLOGY 


A  POPULAR  ACCOUNT 
OF  THE  FUNCTIONS 
OF   THE  HUMAN  BODY 


BY 

DR.  ANDREW  WILSON,  F.R.S.E.,  etc., 

COMBE    AND    GILCHRIST    TRUST     LECTURER  ; 

LATE  LECTURER  ON   COMPARATIVE  ANATOMY 

IN  THE  EDINBURGH   MEDICAL  SCHOOL, 

ETC. 


NEW  YORK 

FREDERICK  A.  STOKES  COMPANY, 
PUBLISHERS. 


BIOLOGY 

LIBRARY 

G 


. 
- 

•:          ;'      :.-, 


• 


CONTENTS 


CHAPTER  PAGE 

PREFACE         vii 

I. — THE  STORY  OF  THE  BODY'S  CONSTITUTION  1 

II. — THE  STORY  OF  OUR  FOODS          13 

III.— THE  STORY  OF  DIGESTION            30 

IV. — THE  STORY  OF  THE  HEART           56 

V. — THE   STORY  OF  THE    LUNGS,   SKIN,   AND 

KIDNEYS        77 

VI. — THE  STORY  OF  THE  BRAIN  AND  NERVE...  101 


LIST  OF  ILLUSTRATIONS 


FIG.  PAGE 

1— Human  Skeleton ...  4 

2 — Various  Kinds  of  Body  Cells            ...           ...  ...  7 

3— Goblet  Cells           ...           7 

4— Section  of  Salivary  Gland  ...           ...           ...  ...  9 

5 — Cells  in  which  the  Nerves  of  Taste  end         ...  ...  10 

6— General  View  of  Digestive  Tube      ...           ...  ...  31 

7— Teeth  of  the  First  Set         ...           ...           ...  ...  37 

8— Teeth  of  One  Half  of  Upper  Jaw  in  Position  ...  38 

9— The  Human  Tongue            ...            ...           ...  ...  39 

10— The  Stomach          ...           ...           ...           ...  ...  41 

I  I—Front  View  of  Digestive  Organs  in  situ      ...  ...  47 


280862 


vi.  LIST  OF  ILLUSTRATIONS 

FIO.  PAGE 

12— Section  of  Body  ...  ...  52 

13 — Lymphatics  of  Right  Arm  ...  ...  ...  ...     54 

14 — Diagram  of  the  Course  of  Circulation  ...  ...    58 

15— Capillaries  of  the  Skin        ...  ...  ...  ...    59 

16— Capillaries  and  Body  Cells...  ...  ...  ...  60 

17— Blood  Corpuscles  ...  ...  ...  62 

18— Different  Red  Blood  Corpuscles  63 

19 — A  White  Blood  Corpuscle  of  Man,  showing  how  it 

alters  its  shape  ...  ...  ...  ...    64 

20 — Section  of  Human  Heart  (right  side)  ...  ...  68 

21— Left  Side  of  Heart  of  Man...  ...  69 

22 — Diagram  of  the  Heart's  Action        ...  ...  ...    71 

23 — The  Lungs  in  Position,  viewed  from  the  front  ...    84 

24 — Larynx  or  Voice  Box,  Trachea  and  Bronchi...  ...    85 

25— The  Relations  of  Heart  and  Lungs  ...  ...  ...    86 

26 — Structure  of  Lungs  showing  Bronchial  Tubes  ending 

in  Air  Cells      ...  ...  ...  ...  ...    87 

27— The  Dense  Network  of  Bloodvessels  in  the  Lungs    ...    88 
28 — The  Kidneys  in  Position     ...  ...  ...  ...    95 

29— The  Brain  and  Spinal  Cord  — the  Cerebro-Spinal 

System  ...  ...  ...  ...  ...  102 

30 — View  of  Spinal  ©ord,  showing  its  connection  with  the 

Brain,  etc.  ...  ...  ...  ...  ...  103 

31— The  Base  of  the  Brain  ...  ...116 

32— Section  of  Brain  ...  ...  ...117 

33 — Brain  in  Position   ...  ...  ...  ...  ...  118 

34 — Side  View  of  Brain  and  Convolutions  ...  ...  119 

35 — Section  showing  Structure  of  Eye  ...  ...  ...  125 

36 — Section  through  the  External  Meatus,  Middle  Ear, 

and  Eustachian  Tube  .  ..126 


PREFACE 


THIS  Manual  is  intended  to  familiarize  the 
general  reader  with  the  outlines  of  the  Science 
which  deals  with  the  body  in  action,  and  which 
describes  the  working  of  life's  mechanisms.  In 
its  preparation  the  author  has  kept  in  view  the 
possibility  of  the  work  being  useful  as  a  text-book 
for  Senior  Classes  in  Physiology  at  School.  As 
the  whole  foundation  of  the  knowledge  of  Health- 
Science  must  rest  upon  the  basis  afforded  by  an 
acquaintance  with  the  body's  functions,  this  volume 
may  also  appeal  to  students  of  Hygiene. 


vn 


Human  Physiology 

CHAPTER   I 

THE   STORY  OF  THE   BODY'S  CONSTITUTION 

INTRODUCTORY. — In  investigating  the  history  of  a 
new  country  one  naturally  pays  attention  first  of  all 
to  the  constitution  of  the  land  and  to  the  manner  in 
which  it  is  governed  and  its  affairs  regulated  and 
controlled.  Thus  the  nature  of  the  government,  the 
duties  and  privileges  of  citizens,  modes  of  taxation, 
and  even  the  past  history  of  the  people,  are  all 
items  necessary  to  be  studied  before  a  full  and 
complete  knowledge  of  a  country  can  be  obtained. 
If  we  apply  this  comparison  to  the  case  of  the 
human  body  we  shall  find  many  points  of  similarity 
between  the  two  studies.  It  is  impossible  to  gain  an 
adequate  idea  of  such  a  complex  piece  of  organisa- 
tion as  is  represented  by  the  body  of  any  animal 
of  high  rank,  and  more  especially  that  of  man, 
without  first  of  all  taking  a  broad  and  comprehensive 
view  of  its  constitution.  By  constitution,  in  this 
sense,  is  implied  the  nature  of  its  build  and  the 
manner  in  which  its  various  duties  and  actions  are 
performed  and  in  which  its  life  is  regulated.  Far 
more  complicated  than  any  mechanisms  of  man's 
own  invention  are  those  comprised  within  the  limits 
of  his  own  frame.  Yet  it  is  possible  to  gain  a 
comprehensive  and  correct  enough  idea  of  our  own 
constitution  through  considerations  which  for  the 

1 


2  HUMAN  PHYSIOLOGY 

most  part  must  be  directed  to  ascertaining  first, 
man's  place  in  nature ;  second,  the  particular  build 
of  the  frame  he  owns. 

MAN'S  PLACE  IN  NATURE. — Man  stands  at  the 
head  of  the  animal  kingdom,  and  as  such  becomes 
in  turn  the  chief  figure  in  the  class  of  animals 
popularly  known  as  "  quadrupeds  "  and  scientifically 
as  "mammalia."  In  turn,  this  class  forms  one  of 
the  five  divisions  of  the  type  of  animals  known  as 
Vertebrates,  or  "  back-boned  "  forms.  In  all  of  these 
animals  the  presence  of  a  back  bone  or  spine  forms 
a  distinctive  feature,  for  even  in  the  very  lowest, 
represented  by  certain  fishes,  if  a  bony  spine  itself 
is  not  developed,  we  find  in  such  animals  a  struc- 
ture representative  of  the  back  bone  itself.  Man's 
superiority  over  all  other  members  of  his  class,  and 
therefore  over  all  Vertebrates,  is  represented  by 
features  which  really  represent  elaborations  or 
evolutions  of  the  structures  found  in  his  lower 
neighbours.  For  example,  the  bodies  of  all  the 
back-boned  animals  are  built  on  one  and  the  same 
type.  If  we  make  a  section,  in  the  long  direction  of 
the  body — of  a  fish,  for  example — we  find  that  the 
skull  and  spine  protecting  the  main  centres  of  the 
nervous  system — brain  and  spinal  cord — occupy 
the  back  or  dorsal  region  of  the  body.  In  the  middle 
we  find  the  digestive  system,  which  is  essentially  a 
tube ;  whilst  situated  lowest  we  find  the  heart. 
Between  the  digestive  system  and  the  back  bone 
there  exists  a  second  nervous  system  known  as  the 
sympathetic  system,  a  structure  typically  repre- 
sented by  a  double  chain  of  nerve-knots  or  centres 
with  connecting  nerves.  Now  this  plan  runs  entire 
and  unbroken  through  the  whole  Vertebrate  series 
of  animals,  from  fish  to  man. 


THE  STORY  OF  THE  BODY'S  CONSTITUTION      3 

If  the  body  of  a  man  be  similarly  bisected,  we  note 
precisely  the  same  arrangement  of  the  great  systems 
of  his  body.  The  back  bone  and  skull  lie  in  the  back 
region,  the  digestive  system  occupies  the  centre  of 
the  body,  and  the  heart  lies  below.  Man,  if  placed 
in  the  same  position  as  the  fish  or  the  dog  and  pro- 
ceeding on  his  hands  and  knees,  is  seen  therefore  to 
represent  a  precisely  similar  type  and  build  of  body 
to  that  of  all  his  vertebrate  neighbours.  The  fact 
that  man,  as  it  has  been  remarked,  is  an  animal 
which  has  taken  to  walking  on  his  hind  legs,  makes 
no  alteration  in  the  disposition  of  those  great  sys- 
tems of  organs.  When  we  speak  of  man's  heart  lying 
to  the  front  of  his  body,  we  merely  mean  that  it  does 
so  because  he  is  a  two-legged  and  erect  animal, 
instead  of  being  a  four-legged  and  therefore  hori- 
zontally placed  creature.  This  remarkable  uniformity 
of  build  of  body  in  the  case  of  back-boned  animals 
is  represented  in  the  case  of  types  of  the  animal 
kingdom  of  lower  grade  than  the  Vertebrates  them- 
selves, so  that  we  awaken  to  the  knowledge  of  the 
fact  that  each  animal,  whatever  be  its  rank  in  the 
scale,  does  not  show  a  body  built  on  a  type  or  plan 
peculiar  to  itself.  On  the  contrary,  it  shares  that 
plan  with  a  larger  or  smaller  number  of  other 
animals  which  constitute  its  so-called  "type"  or  sub- 
division of  the  animal  world  at  large.  Man  is  there- 
fore distinctly  of  the  animal  kingdom,  and  not 
outside  it. 

MAN'S  SPECIAL  FEATURES. — Whatever  special 
features  are  found  to  characterise  the  human  being 
are  simply  to  be  regarded  as  developments  of  the 
common  type  just  described.  In  other  words,  we 
may  safely  assume  that  what  is  specially  human 
reposes  on  the  animal  scaffolding  peculiar  to  the 


HUMAN  PHYSIOLOGY 


whole  back-boned  series.  The  characters  specially 
distinctive  of  man  are  to  be  found  in  the  equal  and 
even  balancing  of  his  head  on  his  spine  (Fig.  1). 
The  head  of  other  animals  has,  so  to  speak,  to  be  tied 

on  to  the  spine — a  feature 
well  seen  in  the  case  of  the 
horse,  for  example,  where 
a  very  strong  band  of  fibres 
constituting  a  ligament, 
literally  ties  the  head  on 
to  the  back  bone.  The 
balancing  of  man's  head 
on  his  spine  without  effort 
has  special  reference  to 
his  upright  position,  as 
also  has  the  particular 
conformation  of  his  back 
bone.  In  the  human  spine 
we  find  a  series  of  curves 
such  as  are  found  in  no 
other  animal,  and  these 
curves  are  specially  adap- 
ted for  the  more  perfect 
support  of  the  head  and 
body  at  large  in  the  erect 
position  which  man  of  all 
animals  can  alone  easily 
and  perfectly  assume. 
With  regard  to  the  curves 
of  the  spine,  it  may  be 
noted  that  these  appear  in 
the  child  after  birth,  and  are  not  fully  completed 
until  some  time  after  the  child  has  risen  from  the 
quadrupedal  position  in  which  it  at  first  crawls  to 
assume  the  erect  and  human  posture.  It  is  a 


Fig.  1.— HUMAN  SKELETON 

Showing  adaptation  to  erect 
posture. 


THE  STORY  OF  THE  BODY'S  CONSTITUTION      5 

fundamental  rule  of  science  that  structures  with 
which  we  are  born  are  those  we  share  in  common 
with  lower  animals,  whereas  conformations  which 
appear  later  on  in  life,  are  to  be  regarded  as 
specially  human.  We  see  the  application  of  this 
doctrine  in  the  case  of  the  curves  of  the  spine. 
Man  develops  these  curves  after  birth  in  relation  to 
his  assumption  of  the  erect  posture,  and  such  curves 
therefore  must  be  regarded  as  distinctly  human  in 
character.  Again,  the  shape  of  man's  haunch  or 
pelvis,  and  the  manner  in  which  the  thigh  bones  are 
jointed  thereon,  indicate  a  distinctive  adaptation  to 
the  erect  posture,  as  also  does  the  manner  of  articula- 
tion or  joining  of  the  end  of  the  thigh  bone  with  the 
leg.  When  we  come  to  consider  man's  feet  we  again 
find  a  special  modification  for  the  erect  posture.  The 
sole  of  the  foot  is  broadened  out,  and  the  heel  bone 
is  especially  prominent — more  prominent  indeed  in 
man,  having  regard  to  the  length  of  the  feet  and 
size  of  body,  than  in  any  other  animal.  The  heel 
bone,  it  will  readily  be  understood,  forms  an  effective 
fulcrum  or  support  for  the  body  in  the  erect  posi- 
tion, and  prevents  any  tendency  to  over-balancing 
in  the  backward  direction.  Such  are  a  few  of  the 
anatomical  characteristics  peculiar  to  man.  If 
we  considered  the  case  of  man's  brain  and  his 
mental  attributes,  we  should  discover  other  and 
even  greater  differences  between  him  and  his 
nearest  animal  relations.  Although  man's  brain  is 
built  up  on  a  general  type  which  is  found  to  run 
through  the  brains  of  all  back-boned  animals,  he 
nevertheless  has  more  highly  developed  than  in  any 
other  creatures  certain  brain  regions,  especially  the 
frontal  or  forehead  region  of  the  brain  which  is 
now  recognised  to  be  the  seat  of  the  higher  brain 


8  HUMAN  PHYSIOLOGY 

functions.  Indeed,  one  might  very  well  correctly 
express  the  opinion  warranted  by  scientific  con- 
siderations, that  if  we  take  into  account  man's 
mental  powers  alone,  dependent  upon  the  possession 
of  a  highly  developed  brain,  these  characters  would 
entitle  the  human  being  to  a  kingdom  to  himself  in 
the  animal  sphere. 

OUR  BODILY  CONSTITUTION. — The  complexity  of 
the  human  body  becomes  resolved  into  a  certain 
degree  of  simplicity,  when  we  discover  that  under 
the  single  personality  which  a  human  being  re- 
presents, there  is  included  all  the  elements  of  a 
compound  commonwealth.  When  the  constitution 
of  the  body  is  closely  scrutinised,  we  find  that 
ultimately  its  component  units  become  resolved  into 
collections  of  microscopic  bodies  to  which  the  name 
of  cells  has  been  given.  In  certain  parts  of  the  body 
it  is  true  there  are  fibres  to  be  found,  these  being 
represented  by  the  muscles  or  flesh  of  the  frame,  by 
the  ligaments  of  bones  binding  them  together  in  the 
joints,  and  by  the  nerve  fibres  of  which  the  nerves 
are  composed,  these  last  representing  the  telegraph 
wires  of  the  body  conveying  messages  to  and  from 
the  external  world.  But  as  fibres  themselves  origin- 
ate from  cells,  and,  what  is  more  to  the  point,  as  the 
whole  body  to  start  with  is  developed  from  one  single 
cell  known  as  the  ovum  or  egg,  we  may  readily 
understand  how  the  cell  may  be  taken  as  the  typical 
unit  of  the  whole  body.  Hence  the  history  of  cells 
forms  the  starting  point  for  all  satisfactory  con- 
siderations which  deal  with  the  body's  constitution. 

THE  CELL. — The  modern  conception  of  the  cell  is 
that  of  a  microscopic  speck  of  protoplasm  or  living 
matter  which  may  vary  from  the  1 -120th  part  of  an 
inch  in  diameter — a  size  represented  in  the  ovum  or 


THE  STORY  OF  THE  BODY'S  CONSTITUTION      7 


egg — to  the  1 -6,000th  or  even  the  1-1 0,000th  part  of 
an  inch;  dimensions 
of  these  last  found  in 
certain  of  the  brain 
cells.  Other  cells 
(Fig.  2)  may  vary 
from  the  1 -200th 
part  of  an  inch  in 
diameter  to  the 
l-25th  part  of  an 
inch;  but  all  cells,  it 
will  be  understood, 
are  microscopic  ob- 
jects, and  can  only 
be  seen  and  studied 
by  the  aid  of  a 
microscope  of  fairly 
high  power  (Fig.  3). 


Fig.  2.— VARIOUS   KINDS  OP 
BODY  CELLS 

Including  those  found  in  mouth  (F), 

windpipe  (CD),  digestive  system  (A), 

eye  (B),  and  brain  (E). 


ABOUT  CELLS. — The  cell  being  thus  a  speck  of 
protoplasm  is,  in  its  essential  nature,  a  living  thing. 
This  fact  must  not  be  lost  sight  of,  even  with  the 
knowledge  that  cells  undergo  in  the  course  of 

their  development  special 
changes,  many  of  them 
dying  and  perishing,  to  be 
replaced  by  other  cells, 
whilst  others  again  may 
become  more  or  less 
hardened  and  take  part 
in  the  formation  of  bodily 
structures  which  can 
scarcely  be  called  vital  in  their  nature.  The  cells 
which  compose  the  epidermis  or  outer  layer  of  the 
skin,  for  example,  are  produced  from  the  upper  sur- 
face of  the  under-skin.  As  layer  after  layer  of  these 


Fig.  3.-— GOBLET  CELLS 

Found  in  the  intestine  or 
bowel. 


8  HUMAN  PHYSIOLOGY 

cells  is  formed  and  pushed  upwards,  the  outermost 
layers  become  dried  and  scale-like,  and  are  given  off 
from  the  surface  of  the  skin  in  large  numbers,  being 
worn  away  by  the  friction  of  our  clothes,  and  also 
being  removed  in  the  act  of  washing.  The  history 
of  a  skin  cell  therefore  indicates  in  a  measure  the 
history  of  many  of  the  living  units  of  our  body. 
They  begin  as  living  vital  structures,  and  pass,  as 
the  body  itself  does,  through  a  stage  of  decline  and 
finally  of  death.  Included  in  the  living  substance  of 
a  cell  we  usually  find  a  solid  particle  termed  the 
nucleus,  and  attached  to  or  imbedded  in  the  surface 
of  this  latter  a  smaller  particle  termed  the  nucleohis. 
These  are  highly  important  structures,  which, 
however,  need  not  further  be  alluded  to  in  the 
present  instance,  save  to  remark  that  they  are 
closely  connected  with  the  production  of  new  cells. 
Many  cells,  in  addition,  possess  a  cell  wall  or 
boundary-membrane,  although  this  last  item  does 
not  appear  to  be  an  essential  characteristic  of  many 
of  the  living  units  of  our  frames. 

THE  WORK  OF  CELLS. — Recognising  the  cell  as 
a  living  structure  in  its  most  typical  aspect,  we  must 
further  note  that  every  important  organ  and  tissue 
of  our  frame  is  composed  of  cells.  Naturally,  as  in 
a  State  there  are  different  grades  of  citizens,  some 
performing  work  of  a  higher  grade  than  others,  so 
in  our  bodily  constitution,  we  find  that  whilst  the 
whole  duties  of  the  body  are  performed  through  the 
work  of  these  wonderful  cells,  there  naturally  appear 
variations  in  the  relative  importance  of  our  living 
units.  The  cells  which  compose  the  outer  layer 
of  the  skin  are  thus  relatively  unimportant  as 
compared  with,  say,  the  cells  of  which  the  liver  is 
composed,  or  when  compared  with  those  which 


THE  STORY  OF  THE  BODY'S  CONSTITUTION      9 

manufacture  or  secrete  the  gastric  juice  of  the 
stomach,  those  which  manufacture  the  sweetbread 
juice,  or  those  which  secrete  the  saliva  of  the 
mouth  (Fig.  4)  or  the  tears  supplied  by  the  tear 
glands  of  the  eyes.  More  important  still,  in  respect 
of  the  duties  they  perform,  are  nerve  cells,  those 
which  constitute  the  units  of  the  nervous  system 
(Fig.  5)  or  governing  system  of  the  body,  amongst 
which  fall  naturally  to  be  included  the  brain  cells. 


Fig.  4. — SECTION  OF  SALIVARY  GLAND 

Showing  cells  lining  the  duct  (b),  and  others 
situated  in  the  gland  substance. 

We  may  regard  the  living  matter  of  which  nerve  cells 
are  composed  as  representing  the  highest  form  of 
protoplasm  which  is  known.  If  we  are  to  judge  the 
character  of  living  matter  by  the  duties  it  performs, 
it  is  obvious  that  the  living  matter  of  a  brain  cell, 
engaged  in  the  work  of  bodily  government,  must 
be  of  a  vastly  superior  character  to  that  which 
devotes  its  energies  to  the  manufacture  of  bile  or 


10 


HUMAN  PHYSIOLOGY 


of  sweetbread  juice.  Hence  the  relative  importance 
of  cells  is  a  point  to  be  kept  in  mind,  although  we 
must  not  lose  sight  of  the  fact  that  all  cells  are  in 
their  way  necessary  and  important,  each  discharging 
its  own  duty  in  the  maintenance  and  upkeep  of  the 
frame  of  which  it  forms  part.  The  work  of  cells 
is  identical  with  the  work  of  the  body  at  large. 
They  may  be  said  to  represent  the  workmen  of  the 
frame  whether  their  labour  is  devoted  to  supervising 
its  nutrition,  to  governing  its  interests,  or  to  assist- 
ing in  building  up  the  bodily  tissues.  Every- 
thing that  is  made  in  the  body  for  the  body's  use, 
secreted  or  manufactured  in  fact  from  the  blood  as 


Fig.  5.— CELLS 
In  which  the  nerves  of  taste  end, 

the  raw  material,  has  to  be  regarded  as  representing 
the  work  of  cells.  In  the  earlier  stages  of  bodily 
development  the  whole  frame  is  represented  by  a 
mass  of  cells.  Where  strong  structures  in  the 
shape  of  bone,  muscle-fibres,  ligaments  and  the  like 
have  to  be  developed,  we  meet  with  such  structures 
directly  originating  from  cells  themselves.  The 
broad  view  which  may  be  taken  therefore  of  the 
constitution  of  the  human  body  is  that  of  regarding 
it  as  a  really  compound,  or,  as  we  might  term  it, 


THE  STORY  OF  THE  BODY'S  CONSTITUTION    11 

a  colonial  organism.  It  masks  its  compound  nature 
under  the  guise  of  a  single  living  personality,  but 
the  Ego  which  every  man  represents  in  himself  is  a 
compound  thing,  and  can  only  be  maintained  as  a 
single  personality  through  the  direct  co-operation  of 
the  millions  of  different  cells  of  which  his  body  is 
built  up.  Such  a  broad  view  of  matters  serves  to 
convey  to  us  an  adequate  idea  of  the  constitution  of 
the  living  frame.  If  we  extend  our  glance  through 
the  animal  and  plant  worlds  at  large,  we  may 
discover  that  the  same  remarks  apply  to  all  other 
living  organisms.  The  very  lowest  animals  and 
plants  consist  each  of  a  single  cell.  The  animalcule 
in  the  pool  and  the  yeast  plant  respectively  illustrate 
this  fact.  When  we  advance  beyond  these  lowest 
organisms  we  find  that  the  single-cell  state  gives 
rise  to  the  many-celled  condition.  Hence  the  lowest 
animals  and  plants  are  termed  unicellular,  whilst 
other  and  higher  forms  are  termed  multicellular. 
On  this  basis  we  may  recognise  that  man  stands  at 
the  head  of  the  multicellular  animals,  not  the  least 
interesting  fact  involved  in  this  statement  being  that 
already  noted  which  teaches  us  that  our  wonderful 
frame  arises,  like  that  of  all  other  animals  and  plants, 
from  a  single  cell.  It  is,  in  fact,  the  wonderful  mul- 
tiplication of  this  single  cell  we  term  the  ovum  or 
egg  into  all  the  other  cells  of  the  body,  which 
constitutes  one  of  the  most  remarkable  facts  of 
living  existence. 

THE  BODY'S  CHEMICAL  COMPOSITION. — A  word 
regarding  the  chemical  composition  of  the  body  may 
be  added  here.  There  are  to  be  discerned  in  man's 
body  some  fourteen  elements,  all  of  them  common  to 
the  world  at  large.  They  are  represented  by  oxygen, 
carbon,  nitrogen,  hydrogen,  lime,  potash,  soda, 


12  HUMAN  PHYSIOLOGY 

sulphur,  iron,  phosphorus,  magnesium,  and  other  less 
familiar  substances.  Our  elements  therefore  pre- 
sent nothing  distinctive.  These  elements  combine, 
moreover,  to  form  compounds.  Some  of  the  latter 
(water,  common  salt,  phosphate  of  lime,  chalk,  etc.) 
are  also  common  in  the  world  around  us ;  but  other 
compounds,  formed  by  the  elements  noted  (proto- 
plasm or  living  matter,  fat,  starch,  sugar,  etc.)  are 
peculiar  to  animals  and  plants.  It  is  this  power  of 
building  up  the  latter  class  of  compounds  which  dis- 
tinguishes living  beings.  The  body  of  a  man,  taking 
it  at  100,  is  composed  of — water,  61*0  per  cent; 
minerals,  5*5;  bony  matter,  18'0;  starch  and  sugar, 
O'l ;  and  fat,  15*4. 


THE  STORY  OP  OUR  POODS  13 


CHAPTER    II 

THE    STORY    OF    OUR    FOODS 

THE  DEMAND  FOR  FOOD. — To  nourish  ourselves 
is  the  first  duty  we  perform  on  entering  the  world, 
and  it  is  the  last  we  discharge  on  leaving  it.  All 
through  life  exists  the  necessity  for  finding  our 
daily  bread.  Nor  is  this  a  feature  peculiar  to  man 
alone.  The  fungus  growing  on  the  wall,  the  lofty 
tree,  the  animalcule  in  the  pool,  and  the  higher 
animal,  through  their  whole  existence  must  be  fed. 
Indeed,  if  one  were  to  try  to  discover  the  sharpest 
line  of  demarcation  which  might  be  drawn  between 
the  world  of  life  and  that  of  non-living  matter,  we 
should  find  it  in  this  perpetual  demand  for  food  on 
the  part  of  the  animal  and  plant.  Growth  of  a  kind 
is  certainly  represented  in  the  world  of  non-living 
matter.  A  stalactite  or  lime  pillar  depending  from 
the  roof  of  a  cave  will  grow,  but  it  enlarges  its  size 
simply  by  additions  to  its  outside  surface,  and 
stoppage  of  this  process  of  accretion,  as  it  is  called, 
has  little  or  no  effect  on  the  stability  of  the  object. 
The  case  is  very  different  with  a  living  being.  Not 
merely  is  a  constant  supply  of  food  demanded,  but 
the  material  taken  as  nutriment  is  received  into  the 
interior  of  the  organism,  and  has  to  undergo  a 
process  of  digestion  whereby  it  is  assimilated  and 
ultimately  changed  into  the  substance  of  the  living 
being  itself.  In  this  latter  respect  we  again  perceive 
a  very  striking  difference  between  living  things  and 


14  HUMAN  PHYSIOLOGY 

things  that  are  inorganic  or  non-living  in  their 
nature.  A  geranium  growing  in  a  pot  illustrates 
equally  with  man  the  necessity  for  a  constant  food- 
supply.  The  plant  will  draw  from  the  air  so  much 
carbonic  acid  gas,  which  is  absorbed  by  its  leaves. 
By  its  roots  it  will  take  up  from  the  soil  water, 
minerals,  and  also  a  certain  amount  of  ammonia; 
these  items  constituting  the  food  of  the  green  plant. 
The  failure  to  supply  any  of  these  items  will  result 
in  the  death  of  the  plant  from  a  want  of  nourish- 
ment, and  if  we  turn  to  the  animal  the  same  remark 
applies.  Its  food  is  certainly  different  from  that  of 
the  plant,  but  whatever  be  the  kind  of  nourishment 
necessary  for  the  animal,  that  nutriment  must  be 
supplied,  otherwise,  like  the  plant  deprived  of  water 
and  other  food,  the  existence  of  the  animal  will 
assuredly  come  to  an  end. 

WHY  WE  EAT  OUR  DINNER. — Associated  with  this 
demand  for  food,  another  consideration  crops  up  in 
the  shape  of  the  inquiry  why  food-taking  should 
represent  a  necessary  duty  of  the  living  being  at  all. 
From  a  social  point  of  view  we  might  argue  that  had 
we  been  differently  constituted,  a  very  large  number 
of  our  fellow-beings  might  find  existence  a  somewhat 
easier  matter  than  it  proves  to  be.  There  is  a  con- 
stant struggle  on  the  part  of  many  human  beings  to 
obtain  food ;  hence,  if  the  duty  of  getting  food  were 
removed,  their  existence  might  prove  a  less  arduous 
period  than  is  represented  to-day.  It  is  easy  to  show 
that  the  inexorable  laws  of  nature,  which  have  to  be 
obeyed  lest  the  penalty  of  disease  and  death  come 
upon  us,  are  founded  upon  a  very  plain  and  distinc- 
tive feature  of  the  living  constitution.  An  answer 
to  the  question,  "  Why  do  we  want  our  dinner?"  is 
perhaps  not  so  easily  or  satisfactorily  supplied  as 


THE  STORY  OF  OUR  FOODS  15 

might  be  imagined.  To  say  that  we  eat  because  we 
are  hungry  and  drink  because  we  are  thirsty,  only 
doubles  the  difficulty  which  before  was  single ;  for 
the  inevitable  inquiry  would  follow  in  the  shape  of 
the  question,  "  Why  are  we  hungry  and  why  are  we 
thirsty?" 

THE  ANSWER. — A  comprehensive  view  of  life, 
founded  upon  scientific  knowledge,  teaches  us  that 
our  body  is  a  machine  that  is  always  working.  It 
requires  very  little  thought  to  convince  us  of  the 
truth  of  this  statement.  When  we  go  to  sleep,  for 
example,  and  seek  to  recuperate  our  worn-out  forces 
in  the  repose  of  the  night,  our  heart,  even  though 
its  work  lessens,  still  continues  to  beat ;  our  chest  rises 
and  falls  in  the  act  of  breathing ;  and  certain  organs 
of  our  body,  such  as  the  liver,  although  their  work 
is  slowed  down,  continue  to  act  through  the  watches 
of  the  night.  There  are  certain  of  our  brain  cells, 
which,  representing  the  night  shift  of  the  workmen 
of  the  nervous  system,  keep  watch  and  ward  over 
our  destiny.  Thus,  even  in  sleep  the  work  of  the 
body  is  not  suspended.  Its  bodily  work  is  continued 
with  increased  force  during  our  waking  life,  and,  in 
addition,  we  are  then  face  to  face  with  another  fact, 
namely,  that  the  work  we  have  to  do  in  the  world  is 
superadded  to  that  represented  by  the  mere  bodily 
labour  of  maintaining  our  life.  We  are  therefore 
encompassed  and  environed  by  a  continual  atmo- 
sphere of  bodily  work  and  labour.  It  is  of  course 
an  undeniable  axiom  that  all  work  means  waste. 
The  waste  attending  the  work  of  any  ordinary 
machine  is  represented  in  two  forms.  In  the  first 
instance,  there  is  waste  of  the  actual  machinery 
itself:  the  substance  of  the  machine  undergoes 
wear  and  tear.  But  there  is  also  a  constant 


16  HUMAN  PHYSIOLOGY 

expenditure  of  its  energy,  which  we  may  define  as  the 
power  of  doing  work.  Obviously,  if  the  machine's 
work  is  prolonged  to  a  certain  extent,  it  will  require 
to  be  supplied  with  additional  material  out  of  which 
it  will  repair  its  own  waste,  and  from  which  it  will 
derive  a  new  store  of  working  power.  In  the  case 
of  an  ordinary  engine,  the  power  of  doing  work  is 
derived  from  the  combustion  of  coal  and  the  con- 
version of  water  into  steam,  whilst  there  is  also  to 
be  considered  a  certain  amount  of  actual  wear  and 
tear  of  the  engine  itself.  Both  sources  of  waste 
have  to  be  reckoned  with,  and  have  to  be  made  good 
by  repairs  to  the  engine  and  by  a  constant  supply  of 
coal  out  of  which  its  energy  is  developed.  Now,  our 
bodies  are  closely  related  to  the  engine  in  respect  of 
their  work  and  repair.  Our  frames  do  not  merely 
demand  food  in  order  that  the  waste  of  the  body  may 
be  repaired  and  replaced  by  new  material,  but  they 
also  require  nutriment  that  they  may  develop  new 
supplies  of  energy  for  the  work  they  have  to  perform. 
In  these  considerations  is  found  the  answer  to  the 
question,  "Why  do  we  eat  our  dinner?"  We  take 
food — in  other  words — because  out  of  the  material 
thus  supplied  we  repair  our  bodily  waste,  and  we 
develop  new  stores  of  working  power. 

ABOUT  FOODS. — Bearing  the  comparison  with  the 
engine  in  mind,  we  naturally  divide  the  foods  on 
which  we  exist  into  two  chief  classes.  These  may 
be  described  as,  first,  body-building  or  tissue-forming 
foods,  otherwise  called  nitrogenous  foods ;  and  second, 
energy -producing  foods — these  last  being  also  termed 
non-nitrogenous  articles  of  diet.  This  division  is  a 
perfectly  natural  one.  A  "  nitrogenous "  food  is 
one  which  includes  the  element  nitrogen  in  its 
composition.  The  presence  or  absence  of  this 


THE  STORY  OF  OUR  FOODS  17 

particular  element  makes  all  the  difference  in  the 
world  in  the  character  of  a  food.  For  as  the  living 
matter  or  protoplasm  of  our  bodies  is  a  nitrogenous 
substance,  and  as  protoplasm  is  one  of  the  most 
important  elements  demanding  repair,  these  foods 
therefore  come  to  represent  in  the  most  typical 
fashion  our  body-building  items.  If  we  make  out  a 
list  of  the  substances  on  which  we  subsist,  we  shall 
find  them  to  consist  of  (1)  water,  (2)  minerals, 
(3)  starches  and  sugars,  and  (4)  fats.  These  represent 
the  non-nitrogenous  foods,  while  the  (5)  nitrogenous 
foods  complete  the  list.  Water  and  minerals  are  in 
one  sense  "body-building"  items,  because,  as  we 
shall  see,  water  enters  into  the  composition  of  every 
tissue  and  fluid  of  our  frame,  whilst  minerals  also 
play  an  important  part  both  in  building  and  in  main- 
taining the  welfare  of  the  body.  Nitrogenous  foods, 
on  the  other  hand,  are  represented  by  various 
principles  contained  in  many  foods  derived  both 
from  the  animal  and  plant  worlds,  such  foods 
containing  other  substances  in  addition  to  their 
nitrogenous  matters.  As  examples  of  the  nitro- 
genous class  we  may  take  albumen,  represented  by 
the  juice  of  meat  and  white  of  egg;  casein, 
represented  by  the  curd  of  milk;  gluten,  found  in 
flour  and  vegetable  matters  at  large;  and  legumin, 
specially  found  in  peas,  beans,  and  lentils.  These 
principles  are  associated,  as  has  been  noted,  with 
other  foods.  For  example — in  peas,  beans,  and 
lentils,  we  also  find  starch,  a  certain  amount  of 
fatty  matter,  and  minerals  along  with  water,  which 
last  we  may  take  for  granted  is  found  in  foods  of  all 
descriptions.  Gluten,  found  in  bread,  is  associated 
with  starch,  a  small  amount  of  fat,  minerals,  and 
water.  Beef  and  other  forms  of  flesh-building 

B 


IS  HUMAN  PHYSIOLOGY 

albumens  also  contain  fat  and  minerals  with  certain 
other  substances.  We  thus  see  that  in  ordinary 
modes  of  feeding  we  do  not  take  as  a  rule  any  food 
singly  or  by  itself,  but  in  combination  with  a  number 
of  other  substances  combined  with  it.  It  is  needful 
to  remark  that  whilst  the  distinction  between  foods 
which  go  to  build  up  and  repair  the  bodily  substance 
and  those  which  supply  us  with  energy  or  working 
power  is  a  very  real  one,  nevertheless  no  sharp 
boundary  line  can  be  drawn  in  practice  between  the 
two  classes  of  substances.  It  is  known  that  under 
certain  circumstances  the  body-building  foods  may 
yield  a  certain  amount  of  energy,  and  some 
physiologists  have  argued  that  fat  itself  may 
discharge  the  duties  of  the  tissue-forming  items, 
although  this  latter  view  has  not  received  universal 
support.  The  probability  is  that  the  functions  of 
the  two  foods  are  interchangeable  in  some  degree, 
but  that  in  the  ordinary  healthy  individual  their 
functions  are  more  or  less  limited  to  playing  the 
parts  just  detailed  in  the  nutrition  of  the  body. 

ABOUT  WATER. — The  human  body  consists  by 
weight  of  two-thirds  of  water;  and  this  fact,  sur- 
prising as  it  may  be,  does  not  reveal  the  whole 
importance  of  water  as  a  food.  A  constant  supply 
of  this  fluid  is  required  not  merely  to  give  to  the 
tissues  their  proper  composition,  but  a  further 
supply  is  needed  to  replace  that  which  is  perpetually 
being  used  up  in  the  body  and  excreted  by  the 
lungs,  skin,  and  kidneys.  Furthermore,  water  is 
demanded  for  the  purpose  of  every  vital  action,  and 
it  is  also  necessary  for  the  solution  of  our  solid 
foods  so  that  they  may  be  presented  to  the  digestive 
organs  in  a  shape  which  favours  their  easy  assimila- 
tion. The  importance  of  water  as  a  food  is  also 


THE  STORY  OF  OUR  FOODS  19 

revealed  by  the  fact  that  on  water  alone  (and  of 
course  on  air,  which  is  really  part  of  our  food 
supply)  a  man  may  exist  for  periods  varying  from 
twenty  to  thirty  days  or  more,  whereas,  if  deprived 
of  water  and  solid  food  as  well,  his  existence  would 
probably  end  in  from  six  to  seven  days.  Water  is 
thus  the  only  food  which  will  maintain  existence  for 
a  considerable  period,  having  also  regard  to  the  air 
breathed.  The  quantity  of  water  contained  in  the 
various  organs  and  tissues  of  the  body  is  very  great. 
In  the  blood  90  per  cent  of  water  exists,  and  even  in 
the  brain-substance  a  very  large  amount  of  water  is 
contained. 

MINERALS. — Our  mineral  food-supply  amounts 
on  an  average  to  about  one  ounce  per  day.  The 
minerals  demanded  for  nutritive  purposes  are  repre- 
sented by  phosphate  of  lime,  which  is  of  extreme 
importance  in  early  life,  seeing  that  it  forms  the 
material  from  which  bone  derives  its  hardness. 
Common  salt,  or  chloride  of  sodium,  is  a  necessity  of 
life,  and  appears  to  be  required  not  merely  for  the 
purpose  of  digestion  in  the  stomach,  but  also  seems 
to  be  in  other  ways  a  necessity  for  the  body,  the  blood 
itself  containing  a  fair  amount  of  this  mineral  which 
is  given  off  or  excreted  in  almost  every  fluid  of  the 
body,  ranging  from  the  perspiration  to  the  tears. 
Other  minerals  required  for  the  support  of  the  body 
include  potash — this  mineral  being  apparently  of 
much  importance  seeing  that  a  lack  of  it  gives  rise 
to  the  serious  trouble  known  as  scurvy,  which  is 
inevitably  associated  with  errors  in  diet.  This 
disease  of  old  was  well  known  in  connection  with 
ships  making  long  voyages,  the  sailors  being  fed  on 
salt  meat  in  the  absence  of  fresh  meat  or  vegetables. 
The  salt  meat  alone  could  not  be  regarded  as  the 


20  HUMAN  PHYSIOLOGY 

cause  of  the  scurvy  outbreak,  but  the  lack  of  potash 
in  the  meat.  When  proper  food  is  supplied  contain- 
ing potash,  scurvy  disappears.  Vegetables  contain 
potash,  as  also  do  fresh  meats  and  potatoes;  and  the 
remarkable  fact  was  noticed  that  in  Irish  famines 
where  the  sufferers  had  little  else  than  potatoes  to 
eat,  though  the  people  were  starving  and  emaciated, 
no  scurvy  appeared.  Minerals  thus  enter  intimately 
into  the  compositon  of  the  body,  and  are  demanded 
as  an  essential  part  of  our  diet. 

THE  ENERGY-PRODUCERS. — The  energy-producing 
foods  are  fats,  starches,  and  sugars.  Fats  stand 
out  distinctively  as  heat-producing  foods,  but  it  is  to 
be  noted  that  a  food  which  is  capable  of  producing 
heat  is  also  capable  of  developing  energy  or  working- 
power.  Probably  the  starches  and  sugars  are  more 
effective  as  energy-producers  than  fat,  because  they 
are  specially  supplied  to  the  muscles;  but  the  typical 
diet  must  include  a  supply  of  both  items,  greater 
working  power  being  developed  from  the  combina- 
tion of  fats,  starches,  and  sugars,  than  from  the 
taking  of  one  of  these  foods  only.  Fat  is  an 
extremely  important  item  in  our  diet.  It  is  not 
merely  required  as  part  of  our  bodily  substance, 
being  formed  out  of  starch  and  sugar  chiefly,  but 
likewise  seems  to  play  an  important  part  in  assisting 
the  digestion  of  other  foods,  whilst  it  is  especially 
the  food  of  the  nervous  system.  Starch  and  sugar 
are  derived  from  the  vegetable  world,  which  may 
also  yield  us  forms  of  fatty  food  in  the  shape  of  oils. 
These  two  classes  of  foods,  starches  and  sugars  on 
the  one  hand,  and  fat  on  the  other,  are  closely 
related  in  chemical  composition.  It  is  curious  to 
note  that  the  body  possesses  the  power  of  convert- 
ing starchy  foods  into  fat.  This  is  well  seen  in  the 


THE  STORY  OF  OUR  FOODS  21 

case  of  obesity  or  corpulence,  the  diet  treatment  of 
which  excludes  starches  and  sugars  from  the  dietary 
to  as  great  an  extent  as  possible,  whilst  the  amount 
of  fatty  foods  need  not  be  reduced  to  the  same 
degree.  The  liver  appears  to  be  an  organ  in  which 
the  transformation  of  starchy  foods  into  fats 
specially  takes  place.  When  geese  and  ducks  are 
artificially  fed  upon  maize  (which  contains  a  very 
large  proportion  of  starch),  and  are  prevented  from 
taking  due  exercise,  the  livers  of  the  birds  become 
masses  of  fat,  which  are  used  in  the  preparation  of 
the  familiar  pate  de  foie  gras  of  Strasburg. 

OUR  NOURISHMENT. — One  of  the  first  rules  for 
healthy  nutrition  which  may  be  deduced  from  what 
we  have  learned  regarding  foods,  is  that  both  classes 
of  foods  are  required  for  the  due  nutrition  and 
support  of  the  body,  and  this  for  the  reason  that  the 
one  class  of  foods  discharges  different  functions  in 
the  frame  from  the  other.  The  body-building  foods 
are  not  required  in  anything  like  the  proportion  of 
the  energy-producing  ones.  The  comparison  between 
the  engine  and  the  body  again  holds  good.  The 
engine  in  the  performance  of  its  work  consumes 
far  more  coal  and  water,  as  sources  of  energy- 
production,  than  it  requires  iron  for  repairs,  although 
it  must  be  confessed  the  human  engine  is  somewhat 
more  imperious  in  its  demands  for  the  daily  repair 
of  its  substance  than  is  the  machine.  The  com- 
parison, however,  holds  good  so  far  in  that  day  by 
day  we  must  consume  a  far  larger  amount  of  work- 
producing  foods  than  of  those  which  contribute  to 
renew  our  bodily  substance.  Thus  it  has  been 
calculated  that  the  proportions  required  in  the  case 
of  an  adult  man  of  the  two  foods  are  represented  by 
one  of  nitrogenous  or  body-building  substance  to 


22  HUMAN  PHYSIOLOGY 

four  or  four  and  a  half  of  the  energy-producing 
foods.  We  thus  consume  a  far  greater  amount  of 
starchy  food  and  sugar  than  of  albumen,  casein,  or 
any  of  the  other  foods  which  repair  the  tissues.  In 
the  case  of  hard  work  the  proportions  of  both  have 
to  be  slightly  increased,  but  still  the  working  foods 
must  naturally  assume  a  predominance.  Nature 
teaches  us  much  the  same  lesson  when  we  inves- 
tigate the  composition  of  the  foods  which  she 
especially  employs  for  the  nourishment  and  building 
of  the  young  animal.  The  composition  of  milk 
shows  us  a  perfect  combination  of  the  two  classes  of 
foods  for  the  purpose  of  body-building  and  for 
energy-production.  Milk  contains  not  merely  casein 
or  curd  for  the  formation  of  tissue,  but  likewise  sup- 
plies fat  and  sugar  of  milk,  which  represent  energy- 
producing  substances,  in  addition  to  water  and 
minerals.  The  case  of  the  egg  is  similar.  Out  of  a 
few  teaspoonfuls  of  yolk  and  white  the  body  of  the 
bird  is  built  up,  this  body  exhibiting  a  complexity  of 
structure  not  far  behind  that  of  our  own  frames. 
In  the  egg  we  find  albumen,  fat,  water,  and  minerals  ; 
the  combination  necessary  for  the  building  of  the 
body  being  essentially  that  which  in  after-life  is  also 
required  for  the  body's  support. 

FOOD-TAKING  IN  PRACTICE. — We  have  seen  that 
most  of  the  articles  of  diet  we  consume,  with  the 
exception  of  such  foods  as  water  and  minerals, 
contain  both  classes  of  substances  in  varying  pro- 
portions. The  experience  of  mankind,  apart  from 
scientific  teaching,  has  led  him  to  the  practice  of 
taking  foods  in  such  combination  and  in  such 
proportions  as  usually  on  the  whole  best  conduce 
to  the  nourishment  of  the  body.  In  such  combina- 
tion of  foods  we  receive  the  due  proportions  of  the 


THE  STORY  OP  OUR  FOODS  23 

different  substances  required,  such  proportions  not 
being  offered  by  one  food  taken  by  itself.  Thus, 
white  fish  is  largely  deficient  in  fat,  and  with  this 
article  of  diet  some  form  of  fatty  sauce  is  usually 
taken ;  whereas  on  the  other  hand,  fish  represented 
by  salmon,  herring,  and  eels,  containing  a  fair  pro- 
portion of  fat — eels  especially  containing  much  fat 
— do  not  require  the  addition  in  question.  Salads 
are  made  more  nutritious  by  the  addition  of  eggs 
and  oil ;  and  a  rice  pudding,  deficient  in  fat,  is  made 
a  very  much  more  nutritious  article  of  diet  by  the 
addition  of  eggs  and  milk.  In  the  same  way  foods 
which  are  apt  to  be  somewhat  tasteless  are  rendered 
more  savoury  by  certain  additions  being  made  to 
them.  Thus  with  fowl,  salt  food  in  the  shape  of 
ham  or  bacon  is  taken ;  and  the  familiar  combination 
of  salt  beef  and  greens  is,  in  its  way,  to  be  com- 
mended— the  greens  containing  potash  and  thus 
tending  somewhat  to  modify  the  salt  of  the  beef. 
The  value  of  green  vegetables,  it  may  be  stated, 
does  not  consist  in  their  affording  much  nourish- 
ment, but  in  their  supplying  us  with  the  minerals, 
especially  potash,  which  we  have  seen  to  be  a 
necessary  constituent  of  the  blood.  Even  when  we 
toast  bread  we  cause  it  to  undergo  a  change  which 
converts  so  much  of  its  starchy  contents  into  sugar. 
We  thereby  assist  the  action  of  the  saliva  of  the 
mouth,  the  duty  of  which  is  to  convert  starch  into 
sugar  as  will  be  afterwards  shown.  Such  habits  in 
the  taking  of  food,  as  has  been  said,  have  originated 
as  the  result  more  of  experience  than  of  scientific 
wisdom,  but  science  has  at  least  supplied  reasons 
why  such  combinations  are  beneficial,  and  in  this 
respect  has  given  a  powerful  sanction  to  the  adop- 
tion of  rational  modes  of  feeding. 


24  HUMAN  PHYSIOLOGY 

DIFFERENT  DIETS. — A  question  has  often  been 
asked  regarding  what  has  been  called  "  the  perfect 
way  in  diet."    Science  speaks  here  with  no  uncertain 
voice  regarding  the  great  law  which  underlies  the 
feeding  habits  of  mankind.    Certain  persons  main- 
tain that  vegetarianism  represents  the  ideal  mode  of 
feeding.     Some  of  the  advocates  of  this  system 
subsist  on  milk,  eggs,  and  cheese,  and   are    not 
therefore   to  be    regarded    as  rigid  adherents  to 
their  doctrine.    Others  again  subsist  on  vegetable 
matters  entirely,  whilst  some  extreme  advocates  of 
vegetarianism    reject    most   starchy   articles    and 
advocate  a  diet  which  consists  largely  of  nuts.    It 
may  be  said  that  there  is  no  perfect  way  in  diet 
except  that  which  suits  the  individual  and  is  adapted 
for  maintaining  him  in  perfect  health.    The  great 
law   which    underlies    nutrition    is  that  man  can 
practically  subsist  on  any  kind  of  food,  and  that 
it  is  climate,  or,  in  other  words,  his  position  on  the 
face  of  the  earth  which  determines  the  particular 
articles  of  diet  on  which  he  subsists.    Thus  in  the 
northern  regions  of   the    world    meat    is    largely 
consumed,  and  in  the  far  north  the  diet  is  almost 
exclusively  of  a  fatty  order,  as  represented  in  the 
habits  of  the   Esquimaux.    Here  the  teaching  of 
nature  has  again  been  followed,  for  fat  is  a  typical 
heat-producing  food,  and  the  inhabitants  of  the  Arctic 
regions  therefore  obtain  from  their  diet  a  source  of 
heat  which  external  nature  has  largely  denied  them. 
In  the  south,  on  the  other  hand,  man  tends  to 
become  more  or  less  a  vegetarian  and  fruit-eater, 
because  the  land  he  inhabits  grows  fruits  in  pro- 
fusion, and  vegetables  are  cheap  and  easily  obtained. 
In  the  temperate  climates  of  the  earth  man  becomes 
a  mixed  feeder,  although  certain  nations,  it  is  true, 


THE  STORY  OP  OUR  FOODS  25 

consume  more  meat  than  others.  The  British 
nation  has  been  credited  with  a  larger  consumption 
of  meat  food  than  that  represented  in  any  other 
people.  At  the  same  time  it  must  not  be  forgotten 
that,  with  the  exception  of  those  who  dwell  in  the 
extreme  north,  every  nation  consumes  a  fair  amount 
of  vegetable  matter,  and  the  quantity  of  meat  con- 
sumed cannot,  save  under  exceptional  circumstances, 
be  regarded  as  excessive.  Further,  meat  is  not  by 
any  means  to  be  despised  as  a  body-building  food, 
seeing  that,  although  it  is  an  expensive  diet,  at  the 
same  time  a  little  meat  contains  a  large  amount  of 
body-building  substance,  and  above  all  forms  an 
easily  digested  food.  Indeed,  one  of  the  strongest 
arguments  against  a  purely  vegetarian  diet  is  found 
in  the  facts :  first,  that  such  a  diet  is  apt  to  be  in- 
digestible ;  and  second,  that  a  far  less  proportion  of 
nutritive  substance  is  absorbed  from  a  purely  vege- 
tarian diet  than  from  a  mixed  dietary  in  which 
meats  and  vegetable  foods  are  both  represented. 

EXPERIMENTS  IN  FEEDING  AND  WORK. — It  is 
always  interesting  to  trace  the  history  of  scientific 
discovery  and  to  note  the  manner  in  which  definite 
conclusions  regarding  any  special  subject  have  been 
arrived  at  and  formulated.  The  main  principles 
of  the  science  of  foods  and  feeding  having  been 
detailed,  it  is  on  these  latter  grounds  important  that 
we  should  become  aware  of  the  manner  in  which 
it  was  demonstrated  that  whilst  the  nitrogenous 
foods  are  to  be  regarded  as  body-builders  the  non- 
nitrogenous  foods — starches  and  sugars — fall  to  he 
considered  the  sources  of  our  energy  or  working- 
power.  In  the  days  of  Baron  Liebig,  the  famous 
chemist,  foods  were  classified  as  "body-builders" 
(or  tissue-formers),  and  "heat-producers."  The 


26  HUMAN  PHYSIOLOGY 

fats,  starches,  and  sugars  were  classified  under  the 
latter  category,  but  the  production  of  heat  was  not 
then  associated  in  the  minds  of  scientific  men  with 
the  development  of  energy.  In  other  words,  food 
which  was  regarded  as  a  heat-producing  element 
was  dissociated  from  any  other  of  the  special 
functions  we  know  it  to  discharge  when  consumed 
in  the  body.  Liebig  taught  the  doctrine  that  the 
work  of  the  body  was  done  on  nitrogenous  food. 
He  assumed,  for  example,  in  the  action  of  a  muscle 
fed  by  such  foods,  that  the  muscle  used  up  its 
substance,  and  in  other  words  developed  its  power 
of  movement  or  work  out  of  the  consumption  of  its 
own  material.  This  view  held  the  scientific  field 
for  many  years,  until  various  circumstances  seemed 
to  raise  doubts  in  the  minds  of  physiologists 
regarding  the  correctness  of  Liebig's  views.  Hence 
arose  the  necessity  of  further  experimentation. 
This  was  carried  out  chiefly  by  Continental  scientists 
who  practically  demonstrated  in  a  manner  which 
left  nothing  to  be  desired  that  Liebig  was  mistaken, 
and  that,  as  the  modern  doctrine  of  food-usage  in 
the  body  teaches,  the  nitrogenous  foods  are  the 
typical  body-builders,  whilst  the  non-nitrogenous 
foods  are  those  which  represent  the  coal  or  source 
of  energy  of  the  human  machine. 

THE  DEMONSTRATION. — A  series  of  experiments 
made  by  two  Swiss  observers  stands  out  prominently 
as  illustrating  the  nature  of  the  researches  which 
gave  information  of  paramount  importance  regard- 
ing diet  to  the  world  at  large.  Their  experiments 
were  made  at  the  Faulhorn  Mountain  in  Switzerland. 
They  endeavoured  by  practical  work — taking  them- 
selves as  the  subjects  of  the  experiments — to 
discover  the  nature  of  the  foods  which  were 


THE  STORY  OF  OUR  FOODS  27 

specially  consumed  in  the  act  of  bodily  work. 
Estimating  the  height  of  the  Faulhorn  Mountain  as 
10,000  feet,  the  basis  of  their  experimentation  took 
the  shape  of  the  investigation  of  the  amount  of 
bodily  waste  given  off  by  a  man,  weighing  140  pounds, 
climbing  the  mountain.  This  of  course  represented 
a  measured  piece  of  work:  the  raising  of  a  man's 
own  weight  (140  pounds)  10,000  feet  high.  Paying 
attention  to  the  amount  of  waste  matter  which 
was  given  forth  in  the  accomplishment  of  this 
task  as  compared  with  that  excreted  at  rest,  they 
arrived  at  certain  definite  conclusions.  We  have 
to  bear  in  mind  that  as  the  two  classes  of  foods 
are  used  up  in  the  living  body,  two  different  kinds 
of  waste  are  given  forth  as  the  result.  The  nitro- 
genous foods  give  off  waste  chiefly  by  the  kidneys, 
this  waste  material  being  represented  by  a  substance 
known  as  urea,  which  represents  in  itself  the  final 
stage,  so  to  speak,  in  the  breakdown  of  nitrogenous 
substance  in  the  body.  On  the  other  hand,  the 
waste  of  the  non-nitrogenous  foods  is  represented 
by  substances  given  forth  from  the  lungs,  skin, 
and  in  part  by  the  kidneys.  These  are  in  chief, 
heat,  water,  and  carbonic  acid  gas.  The  problem 
being  thus  fairly  defined,  the  two  experimenters 
carefully  calculated  the  amount  of  waste  of  the 
two  kinds  specified  during  their  periods  of  rest 
and  during  their  climbing  of  the  mountain  respec- 
tively. The  result  was  the  discovery  that  the 
amount  of  urea,  that  is,  the  waste  of  nitrogenous 
food,  did  not  materially  alter  whether  they  were  at 
rest  or  whether  they  were  engaged  in  their  active 
exercise.  On  the  other  hand,  the  waste  of  non- 
nitrogenous  kind  increased  very  materially  during 
their  periods  of  activity,  and  decreased  during  their 


28  HUMAN  PHYSIOLOGY 

time  of  inaction.  These  experiments,  repeated  and 
verified,  clearly  showed  that  the  nitrogenous  waste 
bore  no  proportion  whatever  to  the  amount  of 
exercise  or  work  performed,  and  that  whereas  the 
non-nitrogenous  waste  did  bear  a  very  distinct 
relationship  to  work,  it  became  clear  that  the  non- 
nitrogenous  foods  represent  the  true  source  of 
energy.  In  this  way  the  doctrine  was  firmly  estab- 
lished that  it  is  on  fat,  starch,  and  sugar,  that  our 
active  bodily  work  is  performed,  whilst  nitrogenous 
foods  became  settled  in  their  proper  place  as  tissue- 
producers  and  repairers  of  the  bodily  waste  which 
to  a  certain  extent  is  perpetually  represented  in  our 
frames. 

AN  INTERESTING  TABLE. — An  interesting  table 
was  compiled  by  the  late  Dr.  Frankland,  the  eminent 
chemist,  on  the  results  of  the  experiments  just 
described.  He  calculated  the  quantity,  the  cost  per 
pound,  and  the  actual  cost  of  the  food,  which,  if 
perfectly  consumed  and  utilised  within  the  human 
body,  would  supply  it  with  energy  enough  to  raise 
a  man's  weight  (140  pounds)  10,000  feet  high.  The 
following  items  represent  the  chief  particulars  of  the 

calculations  thus  made : — 

Total 
Cost. 
8.  d. 

0  3J 

0  3J 

0  5J 

0  5} 

0  11* 

1  Oi 

3  6i 

4  6 
From  this  table  it  appears  clear  that  the  non- 


Price 

Ibs. 

per  Ib. 

d. 

Bread 

2*345      ... 

li 

Oatmeal  ... 

T281       ... 

2* 

Potatoes  ... 

5*068       ... 

1 

Beef  Fat... 

0*555      ... 

10 

Cheese     ... 

1*156       ... 

10 

Butter     ... 

0*693       ... 

1*6 

Lean  Beef 

3*532       ... 

ro 

Pale  Ale  . 

9  bottles  ... 

0*6 

THE  STORY  OF  OUR  FOODS  29 

nitrogenous  foods  come  to  the  front  as  energy- 
producing  substances.  The  popular  idea  that  the 
best  food  on  which  to  feed  a  man  having  a  fair 
amount  of  physical  work  to  do  is  beef-steak  or  other 
form  of  meat,  is  shown  to  be  erroneous.  The  meat 
is  valuable  enough  as  a  tissue-former,  but  as  shown 
by  Dr.  Frankland's  table,  the  working-power  which 
the  meat  affords  can  only  be  got  out  of  the  fat  it 
contains;  and  in  the  case  of  lean  meat  a  large 
quantity  of  this  substance  would  require  to  be  eaten 
to  afford  the  necessary  supply.  These  researches 
also  teach  us  economy  in  the  use  of  food.  The 
combinations  of  food  already  alluded  to  are  economi- 
cal in  that  one  food  supplies  what  another  food 
lacks.  A  man  fed  on  a  proper  quantity  of  bread  and 
meat  would  diet  himself  more  economically  than  if 
he  took  meat  alone,  or  bread  alone — economically, 
that  is,  in  respect  of  his  obtaining  sufficient  material 
for  his  support.  The  bread  and  meat  together  in 
suitable  quantities  would  supply  him  with  both  body- 
building food  and  with  energy-producing  food  in  the 
shape  of  the  starch  of  the  bread,  as  well  as  the  fat 
of  the  meat.  If  he  took  meat  alone  to  gain  sufficient 
working-power,  he  would  over-load  his  body  with 
nitrogenous  matter  to  obtain  the  bare  amount  of  fat 
for  energy-production.  If,  on  the  other  hand,  he 
elected  to  subsist  on  bread  alone,  he  would  greatly 
over-load  himself  with  starch  in  order  to  obtain 
just  sufficient  body-building  substance  found  in  the 
gluten  of  the  bread.  Teachings  of  such  a  kind  are 
of  great  importance  to  the  nation  as  showing  forth 
the  basis  of  economical  feeding  and  as  tending  to 
prevent  the  large  amount  of  waste  of  food  which, 
it  is  to  be  feared,  is  too  commonly  represented  in 
our  midst. 


80  HUMAN  PHYSIOLOGY 


CHAPTER  III 

THE   STORY  OP  DIGESTION 

WHAT  DIGESTION  Is. — A  common  notion  regarding 
the  nature  of  digestion  is  that  which  defines  it  as 
the  work  of  converting  food  into  blood.  This  is  an 
entirely  erroneous  definition.  Food  is  not  con- 
verted into  blood,  but  is  changed  by  digestion  into 
such  a  form  that  it  can  be  added  to  the  blood  and 
be  readily  incorporated  with  that  fluid  with  which  in 
due  season  it  becomes  identical.  It  might  truly  be 
said  that  in  many  respects  the  food  we  eat  presents 
a  certain  chemical  resemblance  to  the  blood  itself, 
but  whilst  digestion  involves  certain  actions  of  a 
physical  kind,  it  is  also  represented  by  a  series  of 
chemical  aspects  wherein  the  elements  of  the  food 
are  recombined  after  being  in  many  cases  split  up 
or  dissociated,  and  thus  made  available  to  renew 
and  repair  the  vital  fluid.  The  blood,  a  topic  to  be 
hereafter  treated,  may  be  regarded  as  the  common 
currency  of  the  body  out  of  which  all  the  tissues  of 
the  body  take  precisely  the  nourishment  which  is 
adapted  to  renew  and  repair  their  vitality,  so  that 
in  one  sense  the  blood  has  been  well  described  as 
being  a  kind  of  fluid  epitome  of  the  body  itself. 

THE  DIGESTIVE  SYSTEM. — It  is  possible  to  form  a 
simple,  and  at  the  same  time  correct,  idea  of  the 
nature  of  any  digestive  system  ranging  from  that  of 
the  lowest  animal,  in  which  such  a  system  appears, 
onwards  to  that  of  man  himself.  Any  digestive 


THE  STORY  OF  DIGESTION 


31 


system  is  really  a  tube  running  through  the  body  of 
an  animal,  having  the  mouth  as  its  anterior  or  front 
opening,  and  the  anus  or  terminal  aperture  of  the 
intestine  or  bowel,  as  its  posterior  opening.  Diges- 
tion may  be  described  as  the  journey  of  food 


•;...  2 


6 


Fig.  6.— GENERAL  VIEW  OF  DIGESTIVE  TUBE 

(1)  gullet,  (2)  stomach,  (3)  beginning  of  intestine, 

(4)  small  intestine,  (5)  large  intestine,  (6)  caecum 

with  appendix,  (7)  rectum. 

along  this  tube,  the  nutriment  in  the  course  of  its 
travels  being  acted  upon  by  various  fluids  or  secre- 
tions poured  upon  it  and  so  changed  and  resolved 


32  HUMAN  PHYSIOLOGY 

for  its  ultimate  destination,  namely,  the  blood 
current.  In  animals  of  simple  organisation  the 
digestive  system  presents  itself  as  a  tube  and 
nothing  more.  In  a  worm,  for  example,  it  exhibits 
pretty  much  the  same  calibre  from  one  end  to  the 
other,  but  in  most  animals  the  width  of  the  tube  is 
found  to  vary  in  different  sections  of  its  length. 
From  the  mouth  we  find  the  first  part  of  the  diges- 
tive tube,  called  the  cesophagus  or  gulltt  (Fig.  6)  lead- 
ing as  a  tube  directly  to  the  stomach.  The  stomach 
itself  is  often  spoken  of  as  a  separate  organ,  and  the 
idea  has  thus  arisen  that  the  stomach  resembles  a 
bag  or  sac  depending  in  the  interior  of  the  body. 
The  true  view  of  the  stomach  is  that  it  is  merely  an 
expanded  part  of  the  digestive  tube;  expanded,  in 
order  that  the  food  may  remain  in  it  for  a  time  so 
that  certain  important  changes,  to  be  hereafter 
chronicled,  may  be  effected  upon  it.  Succeeding 
the  stomach  we  again  come  upon  the  tubular  part  of 
the  digestive  system.  This  portion  is  termed  the 
intestine  or  bowel  (Fig.  6).  In  man  it  is  twenty-six 
feet  long,  and  is  divided  into  two  chief  portions, 
namely,  the  small  bowel  which  immediately  succeeds 
the  stomach,  and  which  measures  twenty  feet  in 
length,  and  the  large  boivel  forming  the  terminal 
part  of  the  digestive  tube,  extending  in  length  to 
about  six  feet.  The  digestive  system,  therefore,  is 
undoubtedly  a  tube,  as  has  been  described,  with  the 
stomach  as  an  expanded  part  thereof. 

DIGESTIVE  GLANDS. — The  length  and  complexity 
of  the  digestive  system  show  a  distinct  relation  to 
the  food  upon  which  an  animal  subsists.  The  rule 
may  be  remembered  that  vegetable-feeding  animals 
possess  longer  and  more  complex  digestive  systems 
than  do  those  which  live  on  a  carnivorous  or  flesh 


THE  STORY  OP  DIGESTION  33 

dietary.  Thus  a  cow's  digestive  system,  or  that  of 
a  sheep,  is  more  complex  than  that  of  the  lion  and 
is  also  much  longer.  The  hen  or  pheasant,  living 
on  grain,  possesses  a  more  intricate  digestive  ap- 
paratus than  the  eagle  or  the  gull,  and  the  same  rule 
applies  to  the  difference  between  the  digestive 
system  of  those  insects  which  live  on  vegetables 
and  those  which  are  carnivorous  in  habits.  It  has 
already  been  noted  that  as  food  passes  along  the 
digestive  tube  certain  secretions  or  fluids  are  poured 
upon  it,  such  as  have  the  result  of  chemically  and 
otherwise  altering  and  changing  it  so  as  to  fit  it  for 
ultimate  addition  to  the  blood.  These  digestive 
fluids  or  secretions  are  provided  by  certain  organs 
termed  digestive  glands.  We  may  figure  these 
glands  as  attached  to  the  sides  of  the  digestive  tract, 
and  as  communicating  in  each  case  with  the  tube 
by  means  of  a  special  duct  or  tube.  The  first  series 
of  digestive  glands  to  be  encountered  are  the 
salivary  glands,  or  those  of  the  mouth.  They  pour 
upon  the  food  the  saliva  or  "  water  "  of  the  mouth, 
the  action  of  which  on  the  food  will  be  presently 
described.  When  the  food  has  passed  into  the 
stomach  the  gastric  glands,  or  those  imbedded  in 
the  wall  of  the  stomach,  pour  out  upon  the  food  the 
gastric  juice  which  is  the  special  secretion  supplied 
by  the  stomach  in  order  to  discharge  its  special 
functions  in  the  act  of  digestion.  When  the  food 
leaves  the  stomach  it  meets  with  other  two  secre- 
tions, one — the  bile — being  poured  upon  it  from  the 
liver,  and  the  other — the  sweetbread  juice — coming 
from  the  pancreas  or  sweetbread,  organs  situated  in 
close  proximity  to  the  stomach  itself.  The  food 
finally  passes  into  the  bowel,  and  having  been  mixed 
with  the  bile  and  sweetbread  juice  is  further 

c 


34  HUMAN  PHYSIOLOGY 

subjected  to  the  action  of  the  secretions  provided  by 
the  glands  of  the  small  intestine  (intestinal  glands) 
which  appear  to  play  some  part  or  other  in  digestive 
action,  the  exact  duty  of  the  secretion  of  the  bowel 
being  as  yet  imperfectly  understood.  We  are  now 
in  a  position  to  review  the  general  conception  of  the 
digestive  system  which,  as  has  just  been  stated,  is  a 
longer  or  shorter  tube  possessing  an  expanded  por- 
tion known  as  the  stomach.  Digestion  is  the  journey 
of  food  along  this  tube,  and  is  accomplished  through 
the  action  of  certain  secretions  or  fluids  contributed 
by  the  digestive  glands  placed  at  the  sides  of  the 
tube,  such  secretions  being  poured  upon  the  food  at 
different  stages  on  its  journey. 

THE  DIGESTIVE  JOURNEY. — Simplifying  thus  our 
view  of  the  process  of  digestion  we  may  divide  the 
digestive  journey  into  three  stages.  The  first  of 
these  concerns  what  happens  to  the  food  in  the 
mouth,  the  second  deals  with  digestion  in  the 
stomach,  and  the  third  and  last  stage  notes  the 
changes  which  the  food  undergoes  in  the  intestine. 
Following  upon  digestion  itself  we  find  another 
function  or  duty,  that  of  absorption.  This  latter 
action  is  devoted  to  the  conveyance  from  the 
digestive  system  into  the  blood  of  digested  food 
which  remains  in  the  intestine,  although,  as  we  shall 
note,  a  certain  amount  of  the  digested  food  leaves 
the  digestive  system  and  passes  into  the  blood  at  a 
stage  considerably  earlier  than  that  representing 
the  close  of  the  digestive  work. 

DIGESTION  IN  THE  MOUTH.  —  That  digestion 
really  commences  in  the  mouth  is  a  fact  not 
generally  appreciated.  Many  persons  speak  of 
digestion  as  if  that  function  was  discharged  by  the 
stomach  alone.  As  a  matter  of  fact,  and  curious 


THE  STORY  OP  DIGESTION  35 

though  the  circumstance  may  appear,  the  stomach 
has  really  very  little  to  do  with  the  digestion  of  food 
at  all,  that  is,  when  compared  with  the  bulk  of  the 
digestive  work  at  large.  The  action  of  the  stomach 
is  no  doubt  highly  important,  but  it  does  not  by  any 
means  include  those  actions  through  which  the 
larger  amount  of  the  diet  is  converted  into  a  form 
ready  to  be  assimilated  by  and  into  the  blood.  The 
first  digestive  work  accomplished  in  the  mouth  is 
division  of  the  food  by  the  teeth.  This  is  an 
extremely  important  action,  but  one  unfortunately 
too  much  neglected  by  the  vast  majority  of  people. 
The  proper  division  of  the  food  by  the  teeth  is 
essential  for  the  healthy  performance  of  digestion, 
first,  because  the  stomach  cannot  digest  masses  of 
food ;  and  second,  because  unless  food  be  thoroughly 
divided  by  the  teeth  it  cannot  be  thoroughly  mixed 
with  the  saliva  which  is  in  itself  an  essential  for  the 
perfect  digestion  of  starchy  foods.  Returning  pres- 
ently to  consider  the  teeth  themselves,  we  may 
illustrate  the  axiom  that  digestion  begins  in  the 
mouth,  by  considering  the  duties  performed  by  the 
saliva  or  "  water  "  of  the  mouth.  This  fluid  is  fur- 
nished by  three  sets  of  glands.  Of  these  glands, 
one  set  exists  in  front  of  the  ears,  these  being  known 
as  the  parotid  glands.  The  other  two  pairs,  called 
sub-maxillary  and  sub-lingual  glands,  are  situated  in 
the  floor  of  the  mouth.  Each  pours  its  secretion 
into  the  mouth  through  a  special  tube  or  duct,  the 
saliva  representing  a  "  secretion  "  as  it  is  termed, 
manufactured  by  cells.  The  essential  units  in  the 
salivary  glands  are  living  cells,  which,  from  the 
blood  supplied  to  the  glands,  elaborate  or  manufac- 
ture the  particular  secretion  afforded  by  these 
organs.  Each  cell  in  this  way  may  therefore  be 


36  HUMAN  PHYSIOLOGY 

regarded  as  a  little  chemist,  seeing  that  secretion 
implies  not  merely  a  separating  from  the  blood  of 
certain  products  already  formed  therein,  but  also 
an  actual  process  of  manufacture  out  of  the  raw 
material  represented  by  the  blood  of  the  new  sub- 
stance or  fluid. 

ABOUT  SALIVA. — This  fluid  in  the  case  of  the 
salivary  glands  is  a  colourless  fluid  consisting  very 
largely  of  water  and  containing  minerals,  while  its- 
chief  constituent  is  a  substance  or  ferment  known 
as  ptyalin.  Upon  the  presence  of  ptyalin  depends 
the  particular  action  which  the  saliva  discharges  in 
the  work  of  digestion.  To  saliva  is  assigned  the 
first  step  in  digestion,  namely,  that  of  converting  the 
starch  we  eat  into  a  form  of  sugar  known  as  grape 
sugar.  This  is  accomplished  by  the  action  of  the 
ptyalin  ferment,  and  we  are  therefore  taught  the 
lesson  that  the  starch  consumed  so  largely  as  food, 
is  intended  by  nature  to  pass  to  the  stomach,  not  in 
the  form  of  starch,  but  in  that  of  a  sugar.  It  may 
be  remembered  that  all  throughout  digestion  this 
rule  holds  good.  Starch,  as  such,  is  practically  use- 
less to  the  body.  It  may  be,  as  we  shall  see,  stored 
up  in  the  liver  in  the  form  of  starch,  but  when 
required  for  bodily  purposes  to  be  applied  to  the 
tissues  as  a  food,  and  especially  to  the  muscles  as 
an  energy-producing  substance,  it  must  be  presented 
in  the  form  of  sugar.  Another  point  worthy  of  im- 
portance, because  possessing  a  distinct  bearing  on 
the  nourishment  of  young  children,  is  the  fact  that 
ptyalin  does  not  appear  in  the  saliva  of  the  child 
until  it  attains  the  age  of  seven  or  eight  months. 
Prior  to  this  age  it  is  therefore  incapable  of  con- 
verting starch  into  sugar,  nature  making  up  for  the 
want  of  starch  by  placing  sugar  ready  made  in  the 


THE  STORY  OF  DIGESTION  37 

milk.  To  giVe  a  child  under  the  age  specified  any 
foods  containing  starch  is  therefore  to  supply  it  with 
material  which  is  not  merely  indigestible,  but  may 
be  regarded  as  being  the  cause  of  a  large  amount  of 
the  infant  mortality  due  to  erroneous  feeding. 

THE  TEETH.— The  importance  of  attending  to  the 

care  of  the  teeth  and  of  preventing  tooth  decay  by 

^ daily  attention  in  the  way  of  brushing  the  teeth  and 


Fig.  7.— TEETH  OF  THE  FIRST  SET 
Showing  the  second  teeth  in  course  of  development. 

cleansing  the  mouth,  scarcely  requires  to  be  incul- 
cated here.  At  the  same  time,  the  duty  of  preserv- 
ing the  teeth  by  all  means  in  our  power  is  one  the 
importance  of  which  should  be  early  impressed  on 
the  minds  of  the  young  by  way  of  avoiding  tooth 
decay  and  tooth  degeneration  which  are  only  too 


38 


HUMAN  PHYSIOLOGY 


conspicuous  features  of  our  age.  The  importance  of 
thoroughly  dividing  the  food  by  the  teeth  has  been 
already  insisted  upon.  Two  sets  of  teeth  (Fig.  7) 
exist  in  man,  and  in  most  of  his  neighbour  animals. 
The  first  teeth  are  known  as  "  milk  teeth,"  and  number 
twenty ;  the  second  set  possessing  twelve  additional 


Fig.  8.-— TEETH  OF  ONE-HALF  OF  UPPER  JAW  IN  POSITION 
Seen  from  above  (a),  and  from  the  side  (fc). 

teeth,  and  therefore  numbering  thirty-two.  In  each 
jaw  the  same  number  and  the  same  arrangement  pre- 
vail (Fig.  8).  There  are  four  front  teeth  or  incisors, 
two  canine  or  eye  teeth,  four  premolars  or  bicuspids, 
and  finally  six  molars  or  back  teeth  in  each  jaw. 


THE  STORY  OF  DIGESTION 


39 


The  last  molars  in  the  jaw  receive  the  name  of 
"wisdom  teeth,"  owing  presumably  to  their  late 
development.  The  six  molars  in  each  jaw  are  not 
preceded  by  any  teeth  in  the  milk  set,  the  presence 
of  the  twelve  molars  thus  accounting  for  the  differ- 
ence in  number  between  the  teeth  of  the  second  and 
those  of  the  first  set.  The  bulk  of  each  tooth  is 
composed  of  a  substance  called  dentine  or  ivory, 
which  is  very  different  from  bone  and  of  much 
denser  texture.  The  top  of  each  tooth  is  coated 
with  a  still  harder  sub- 
stance termed  enamel, 
whilst  at  the  root  we 
find  a  third  substance 
somewhat  resembling 
bone  in  structure  and 
known  as  cement.  The 
teeth,  it  may  be  added, 
are  typically  skin-struc- 
tures, that  is  to  say,  they 
correspond  closely  with 
nails  and  hairs  in  their 
mode  of  origin  and  de- 
velopment, seeing  that 
they  originate  from 
the  delicate  skin  layer, 

which,  folded  inwards  at  the  mouth,  constitutes  what 
is  popularly  known  as  the  gum  or  mucous  membrane. 
SWALLOWING. — Divided  by  the  teeth  and  mixed 
with  the  saliva,  the  food  is  ready  to  be  swallowed. 
This  action  is  somewhat  complicated  in  its  nature. 
It  may  be  briefly  described  as  consisting  first  in  the 
work  of  the  tongue  (Fig.  9)  in  gathering  particles  of 
food  from  all  parts  of  the  mouth  and  gullet  into 
small  masses  or  boluses  suitable  for  swallowing  or 


Fig.  9.— THE  HUMAN  TONGUE 

Showing  the  papillae  or  organs 

of  taste. 


40  HUMAN  PHYSIOLOGY 

deglutition,  as  the  action  is  scientifically  termed. 
The  tip  of  the  tongue  is  next  placed  to  the  roof  of 
the  mouth  and  the  food-mass  tilted  backwards  to  be 
received  and  grasped  by  the  upper  part  of  the  throat 
known  as  the  pharynx.  This  is  a  muscular  bag 
which  is  drawn  up  to  meet  the  food,  the  hinder 
nostrils  at  the  same  time  being  closed  to  prevent  the 
escape  of  any  fluid  from  the  channel  of  the  nose. 
The  food  passing  still  backwards,  reaches  the  Cupper 
part  of  the  windpipe  where  we  find  the  entrance  to 
that  tube  or  passage-way  to  the  lungs  guarded  by  a 
lid-like  structure  known  as  the  epiglottis.  This 
structure,  when  swallowing  is  naturally  performed, 
closes  over  the  windpipe  entrance,  and  the  food 
therefore  passes  over  and  behind  the  windpipe  into 
the  upper  part  of  the  gullet.  The  gullet  itself  is  a 
muscular  tube  whose  walls  are  closely  approximated 
save  during  the  passage  of  food  to  the  stomach. 
Food  does  not  pass  to  the  stomach  by  its  own 
weight  as  is  often  popularly  supposed,  but  is  rather 
squeezed  or  pressed  down  into  the  stomach  by  the 
contraction  of  the  muscles  of  the  gullet  which  act  in 
wave-like  fashion,  ultimately  forcing  food  through 
the  front  opening  of  the  stomach,  called  the  cardia, 
into  that  organ.  Choking,  we  may  perceive,  will  be 
caused  by  any  action  (such  as  speaking  or  coughing) 
which  interferes  during  the  process  of  swallowing 
with  the  perfect  closure  of  the  epiglottis  protecting 
the  entrance  to  the  windpipe. 

THE  STOMACH. — In  man,  the  stomach  (Fig.  10)  is 
a  pear-shaped  expansion  of  the  digestive  tube,  the 
large  end  of  the  pear  lying  to  the  left  side  of  the  body. 
From  the  narrow  end  of  the  pear-shaped  bag  the 
bowel  is  given  off,  this  junction  between  the  stomach 
and  the  bowels  being  found  on  the  right  side  of  the 


THE  STORY  OF  DIGESTION  41 

body  where  the  liver  is  situated.  Roughly  speaking, 
if  we  take  the  stomach  as  the  centre  of  the  organs 
contained  in  the  abdomen  or  belly,  we  find  the  liver 
(Fig.  11)  lying  to  the  right,  the  spleen  to  the  left,  and 
the  sweetbread  or  pancreas  below  and  in  front  of  the 
stomach.  The  stomach,  like  the  rest  of  the  digestive 
system,  has  three  coats  or  coverings.  There  is  first 
of  all  a  somewhat  tough  outer  coating  (serous  coat) 
giving  shape  to  the  tube.  The  middle  coat  is  a 


Fig.  10.— THE  STOMACH 

Showing  interior  and  commencement  of  bowel. 
The  sweetbread  duct  is  shown  opening  into  the  bowel. 

muscular  coat  composed  of  involuntary  muscular 
fibres,  or  in  other  words  of  fibres  which  are  not 
directly  under  the  command  of  the  will  as  are  the 
muscles  of  arms,  legs,  and  other  parts  of  the  body. 
The  function  of  this  muscular  layer  of  the  digestive 
tube  is  naturally  to  propel  the  food  along  its  course, 
whilst  in  the  case  of  the  stomach  the  duty  of  the 
muscular  coating  is  to  cause  movements  of  the 
stomach  to  take  place  so  that  the  food  will  be  made 


42  HUMAN  PHYSIOLOGY 

to  circulate  within  it  and  so  become  thoroughly 
mixed  with  the  secretion  which  the  stomach  pours 
out  upon  it.  The  inner  coating  of  the  stomach,  or 
mucous  layer,  as  it  is  called,  is  that  which  comes  in 
contact  with  the  food.  This  mucous  layer  is  con- 
tinued onwards  into  the  intestine  as  it  appears 
upwards  in  the  gullet.  The  glands  it  contains 
naturally  differ  according  to  the  various  functions 
discharged  at  different  parts  of  the  tube.  It  is  in 
this  mucous  layer  that  the  glands  of  the  stomach 
are  found.  These  are  named  the  gastric  or  peptic 
glands,  each  consisting  of  a  minute  tube  embedded 
in  the  substance  of  the  stomach's  lining  and  opening 
into  the  stomach  by  a  minute  aperture  through 
which  the  secretion  of  the  gland  is  poured  upon  the 
food.  Again  we  come  face  to  face  with  the  work  of 
cells,  for  the  makers  of  the  gastric  juice  of  the 
stomach  are  microscopic  cells  which  line  the  tubular 
glands.  Microscopic  research  has  also  shown  that 
the  cells  deep  down  in  the  glands  differ  from  those 
nearer  the  mouth  of  the  tubes.  The  gastric  juice 
each  gland  secretes  therefore  seems  to  undergo  a 
process  of  elaboration  as  it  advances  from  the  lower 
part  of  the  tube  until  it  is  poured  into  the  stomach. 
GASTRIC  JUICE. — The  gastric  juice  of  the  stomach 
is  a  fluid  of  much  importance.  It  exercises,  as  we 
shall  see,  a  very  definite  action  upon  certain  foods. 
We  find  it  to  consist  of  water,  minerals  (amongst 
which  common  salt  bulks  somewhat  largely),  an  acid 
called  hydrochloric  acid,  and  a  special  ferment  found 
in  no  other  secretion  of  the  body  and  known  as 
pepsin.  The  digestive  action  of  gastric  juice  is  no 
doubt  specially  due  to  the  action  of  the  pepsin  and 
the  acid,  but  at  the  same  time  we  cannot  afford  to 
ignore  the  part  which  may  be  played  in  such  action 


THE  STORY  OF  DIGESTION  43 

by  the  minerals  and  likewise  it  may  be  by  the  water 
represented  in  the  secretion.  The  cubic  capacity  of 
the  adult  human  stomach  is  about  five  pints  and  a 
very  considerable  amount  of  gastric  juice  is  elabor- 
ated and  secreted  in  the  course  of  a  single  day's 
digestive  work.  It  is  interesting  to  note  that  the 
first  accurate  analysis  of  gastric  juice  was  obtained 
from  the  case  of  Alexis  St.  Martin,  a  Canadian 
trapper,  who  early  in  the  nineteenth  century  suffered 
from  a  gunshot  wound  which  penetrated  his  side. 
This  wound  healed  somewhat  too  perfectly  in  the 
sense  that  a  flap  was  left  in  the  man's  side,  and  by 
lifting  this  flap  the  interior  of  the  man's  stomach 
could  be  inspected.  His  medical  attendant,  Dr. 
Beaumont,  recognised  that  this  was  an  exceptional 
opportunity  for  investigating  the  process  of  diges- 
tion. He  accordingly  obtained  samples  of  gastric 
juice  for  analysis  and  likewise  made  many  experi- 
ments with  the  view  of  ascertaining  the  times 
occupied  in  the  digestion  of  various  foods.  Cases 
of  analogous  nature  have  since  occurred,  and  have 
thrown  much  light  on  the  work  of  the  stomach  in 
digestion.  It  may  be  briefly  said  that  vegetable 
foods  are  found  to  require  a  longer  time  for  diges- 
tion than  purely  animal  diet ;  whilst  of  animal  foods, 
fish,  tripe,  and  fowl  appear  to  be  more  readily 
digested  than  meat;  and  amongst  meats,  mutton 
seems  to  be  more  easy  of  digestion  than  beef  and 
pork. 

THE  STOMACH'S  WORK. — Before  food  enters  the 
stomach  its  lining  membrane  is  of  a  pale  pink  hue. 
On  the  entrance  of  food  a  rush  of  blood  takes  place 
to  the  walls  of  the  stomach  in  order  to  supply  the 
raw  material  out  of  which  the  gastric  glands  may 
elaborate  and  manufacture  gastric  juice.  Accord- 


44  HUMAN  PHYSIOLOGY 

ingly,  the  interior  of  the  stomach  may  literally  be 
said  to  blush  on  the  entrance  of  food.  The  gastric 
juice  is  poured  out  upon  the  food,  and  the  stomach's 
movements,  of  which  in  health  we  are  unconscious, 
serve  thoroughly  to  mix  the  food  with  the  secretion 
of  the  organ.  It  would  appear  that  the  food  is  made 
to  circulate  within  the  stomach  in  a  somewhat  figure- 
of-8  fashion,  and  this  again  would  appear  to  proceed 
during  the  whole  period  that  the  food  remains  in 
the  stomach.  The  hinder  aperture  of  the  stomach, 
or  that  which  leads  into  the  intestine,  is  known  as 
the  pylorus  (Fig.  10),  the  aperture  by  which  food 
enters  the  stomach  being  termed  the  cardia,  as  we 
have  already  noted.  The  pylorus  is  kept  closed  by  a 
valve-like  muscular  arrangement  which  exists  in 
that  situation,  and  it  is  only  when  the  proper  time 
arrives  for  the  food  to  pass  out  into  the  intestine — 
that  is,  when  digestion  in  the  stomach  has  been 
completed — that  this  muscular  ring  uncloses,  and  the 
subsequent  contraction  of  the  stomach  forces  the 
digested  material  into  the  bowel. 

WHAT  THE  STOMACH  DIGESTS. — Allusion  has 
already  been  made  to  the  work  of  the  stomach,  in 
respect  that  the  amount  of  its  labours  is  inferior  to 
that  discharged  by,  say  the  bowel  or  intestine. 
Hence  we  now  arrive  at  the  interesting  fact  that 
there  is  only  one  class  of  foods  upon  which  the 
stomach  can  exert  any  decided  action.  These  foods 
are  the  nitrogenous  ones,  represented,  as  we  have 
seen,  by  albumen,  casein,  legumin,  gluten,  and  the 
like.  They  represent  of  course  the  typical  body- 
building elements.  As  by  far  the  larger  proportion 
of  our  daily  meals  consists  of  non-nitrogenous 
starch,  sugar,  and  fat,  it  therefore  follows  that  the 
stomach's  share  in  the  work  of  digestion  is  relatively 


THE  STORY  OF  DIGESTION  45 

small;  if  small,  however,  it  must  be  regarded  as 
nevertheless  of  high  importance.  It  is  not  denied 
that  a  certain  minor  action  on  non-nitrogenous 
starches  and  sugars  may  be  exerted  by  the  stomach, 
but  the  all-important  part  of  its  work  is  the  action 
which  it  exerts  on  nitrogenous  articles  of  diet. 

PEPTONES. — The  gastric  juice  thoroughly  mixed 
with  the  food,  and  leaving  practically  unaltered  the 
sugar  contained  in  the  food  and  any  starch  which 
may  have  escaped  the  action  of  the  saliva  of  the 
mouth  exerts  its  power,  as  we  have  seen,  on  nitro- 
genous articles  of  diet.    Coming  in  contact  with 
albumen  or  any  other  foods  of  this  class  it  converts 
them  into  bodies  known  as  "peptones."     One  of  the 
chief  differences  between  a  peptone  and  the  food  it 
previously  represented  is  that,  as  a  peptone,  it  can 
easily  pass  through  the  walls  of  the  stomach  and 
be  absorbed  by  the    bloodvessels.      The    peptone 
possesses  other  characteristics,  but  this  last  is  the 
special  feature   to  which  attention   may   here    be 
directed.    The  result  is  that  the  peptones  leave  the 
stomach  and  pass  as  described  into  the  bloodvessels 
of  the  organ.    They  then  find  themselves  in  the 
veins  of  the  stomach  which  join  a  very  large  vessel 
known  as  the  "  portal  vein,"  returning  blood  from 
the   whole   of  the    digestive    organs.      In    tracing 
the  course  of  the  portal  vein  we  find  that  it  dis- 
appears into  the  liver,  so  that  the  liver  is  the  direct 
destination  of  the  peptones  which  it  has  been  the 
business  of  the  stomach  to  separate  out  from  the 
rest  of  the  food;  these  peptones,  as  we  have  seen, 
representing  the   changed   nitrogenous   articles  of 
diet  which  have  been  consumed*    What  happens  to 
the  peptones  in  the  liver  will  hereafter  be  described, 
but  it  should  be  noted  that  already  from  the  stomach 


46  HUMAN  PHYSIOLOGY 

we  have  the  absorption  into  the  blood  of  certain 
highly  important  articles  of  food.  It  would  al- 
most seem  as  if  nature  taught  us  the  lesson  that 
the  nitrogenous  foods  required  for  body-building 
purposes  are  of  high  importance,  and,  as  such,  have 
to  be  more  readily  and  quickly  passed  into  the 
circulation;  the  starches,  fats,  and  sugars,  on  the 
other  hand  being  less  important,  and  requiring  to 
wait  for  digestion  in  the  bowel  or  intestine.  The 
stomach  may  be  regarded  in  this  sense  as  a  kind  of 
half-way  house  on  the  digestive  journey  in  which  the 
progress  of  the  food  is  for  the  time  being  arrested 
in  order  that  the  nitrogenous  foods  converted  into 
peptones  should  be  passed  onwards  into  the  liver, 
there  to  be  further  dealt  with  and  fitted  for  their 
ultimate  destination,  namely  the  blood  current. 

THE  LIVER. — The  third  stage  of  the  digestive 
journey  may  be  said  to  commence  with  the  passage 
of  the  food  from  the  stomach  into  the  intestine  or 
bowel.  Immediately  the  food  enters  this  portion  of 
the  digestive  tube  it  meets  with  bile  from  the  liver 
(Fig.  11)  and  sweetbread  juice  from  the  pancreas  or 
sweetbread.  These  two  secretions  are  poured  upon 
the  food  practically  at  the  same  point,  the  duct  or 
tube  from  the  sweetbread  frequently  joining  that 
coming  from  the  liver.  The  liver  is  the  largest 
organ  of  the  body,  weighing  between  three  and  four 
pounds,  and  lying  to  the  right  of  the  stomach  shel- 
tered beneath  the  lower  ribs  of  that  side.  Essentially 
the  liver  is  a  great  colony  of  "hepatic"  or  liver  cells, 
the  diameter  of  each  cell  averaging  the  1-1, 000th 
part  of  an  inch.  Into  the  liver  there  passes  from 
the  great  portal  vein  already  mentioned,  a  continu- 
ous supply  of  blood  returned  from  the  digestive 
organs  at  large.  This  blood,  as  we  shall  see,  is  laden 


THE  STORY  OP  DIGESTION 


47 


with  the  products  of  digestion  in  the  shape  of  foods 
absorbed  from  the  intestine.  On  the  under  surface 
of  the  liver  lies  the  gall-bladder  which  is  a  store- 
house of  bile.  As  the  liver  is  perpetually  secreting 
bile,  and  as  this  fluid  is  not  constantly  demanded  for 
digestive  purposes,  it  is  stored  in  the  gall-bladder 
whence  a  special  duct,  joining  that  coming  from  the 
liver,  conveys  it  to  the  bowel.  The  duties  of  the 


Fig.  11.— FRONT  VIEW  OF  DIGESTIVE 
ORGANS  in  situ. 

liver  are  at  least  threefold.  A  common  conception 
of  this  organ  is  that  it  makes  bile  and  does  nothing 
else.  This  is  a  highly  erroneous  supposition, 
because  the  making  of  bile  represents,  if  it  may  so 
be  termed,  the  least  important  labour  of  the  organ. 
As  it  has  well  been  put,  the  water  discharged  from 
the  engines  of  a  steamer  does  not  represent  the 
work  of  the  vessel,  but  merely  the  result  of  that 
work.  The  secretion  of  bile  similarly  represents  in 


48  HUMAN  PHYSIOLOGY 

reality  a  kind  of  waste  product,  only  a  product  which 
is  made  useful  in  the  economy  of  the  body. 

THE  LIVER  AND  PEPTONES. — The  first  duty  of 
the  liver  is  to  deal  with  the  peptones  or  changed 
nitrogenous  foods  which  we  have  seen  to  be 
conveyed  to  it  from  the  stomach.  The  liver  cells 
deal  with  these  peptones  and  exert  a  certain 
chemical  action  upon  them,  the  effect  of  which  is  to 
change  them  into  a  suitable  form  for  being  added  to 
the  blood.  A  somewhat  curious  point  in  the  history 
of  peptones  refuses  to  be  noted.  If  peptones  them- 
selves were  allowed  to  pass  into  the  blood 
unchanged  from  the  liver,  they  would  give  rise  to 
symptoms  of  body-poisoning,  and  there  seems  little 
reason  to  doubt  that  many  cases  of  so-called  bilious 
disorder  are  really  due  to  interference  with  the 
liver's  work  in  this  respect.  That  our  food,  other- 
wise of  perfectly  healthy  character,  may  therefore 
injuriously  affect  us  if  proper  chemical  changes  are 
not  effected  upon  it  is  obviously  a  remarkable  fact 
of  our  constitution.  The  liver  in  this  respect  might 
be  compared  somewhat  to  a  filter  which  stands 
between  the  food  on  the  one  hand  and  the  blood  on 
the  other.  It  is  a  fact  of  some  interest  in  relation 
to  the  liver's  work  that  actual  poisons  taken  into  the 
body  may  be  detected  in  the  liver  more  readily 
perhaps  than  in  any  other  organ  of  the  body,  the 
liver  exercising  here,  the  same  filtering  action  such 
as  it  discharges  naturally  in  the  process  of  digestion. 

THE  LIVER  AND  SUGAR. — The  second  duty  of  the 
liver  is  that  of  dealing  with  the  sugar-foods  which 
represent  either  sugar  taken  as  such,  or  starches 
which  we  have  seen  are  converted  into  sugar  by 
digestive  action.  From  the  intestine  sugar  is  ab- 
sorbed and  carried  to  the  liver  by  the  portal  vein.  In 


THE  STORY  OP  DIGESTION  49 

the  liver  this  sugar  appears  to  be  converted  into  a 
starchy  substance  known  as  glycogen,  or  animal 
starch.  Stored  up  in  the  cells  of  the  liver,  it  would 
seem  that  this  starch  is  ultimately  reconverted  into 
sugar,  and  paid  out  to  the  blood  by  the  hepatic 
vein  which  represents  the  great  outlet  of  the  liver 
into  the  circulation.  Here  we  might  compare  the 
liver  to  a  banker  who  receives  the  cheques  and 
drafts  of  his  customers,  and  pays  out  money  that  is 
required  in  the  form  of  ordinary  currency  which  can 
be  used  to  pay  the  customers'  workmen.  Some 
doubt  has  been  cast  upon  the  liver's  work  as 
affecting  a  source  of  sugar-supply  for  the  body  at 
large,  and  the  muscles  especially.  It  has  been 
contended  that  the  sugar  which  is  stored  by  the 
liver  is  converted  into  fat,  and  that  any  escape  of 
sugar  from  the  liver  is  to  be  viewed  as  an  unnatural 
process.  This  view,  however,  has  received  but  slight 
support  from  physiologists  at  large.  It  seems  to  be 
refuted  by  the  fact  that  the  hepatic  vein,  carrying 
blood  away  from  the  liver,  contains  a  larger  pro- 
portion of  sugar  than  any  other  vein  in  the  body. 
If  the  sugar-supplying  duty  of  the  liver  be  upheld, 
it  is  not  necessary  to  reject  the  idea  that  the  liver 
may  also  form  fat  from  the  starch  it  stores  up, 
for  we  know  that  starchy  foods  tend  to  produce  fat 
and  are  therefore  forbidden  to  corpulent  persons. 
The  probability  is  that  the  liver  discharges  both 
duties.  It  gives  off  sugar,  and  it  may  form  fat ;  the 
former  action  being  vastly  more  important  than  the 
latter.  A  proof  of  the  liver's  manner  of  dealing  with 
sugar  is  afforded  by  the  disease  known  as  diabetes. 
In  this  disease  there  is  an  excess  of  output  of  sugar 
from  the  liver,  as  well  as  a  certain  want  of  action  on 
the  part  of  the  sweetbread,  the  functions  of  which 

D 


50  HUMAN  PHYSIOLOGY 

will  be  presently  described.  The  result  is  an  excess 
of  sugar-supply  inducing  a  much  enfeebled  condition 
of  body,  associated  with  kidney-trouble,  represented 
by  a  very  much  increased  flow  of  urine.  The  origin 
of  this  disease  is  still  undetermined,  but  it  would 
appear  to  arise  from  some  defect  in  the  working  of 
the  nervous  system  taking  the  shape  of  a  lack  of 
control  over  the  liver  and  its  sugar-producing 
functions ;  a  duty  carried  out  by  some  nerve  centre 
specially  devoted  to  the  regulation  of  the  function  in 
question. 

THE  BILE. — Bile  is  to  be  regarded  as  waste 
matter  which  the  cells  of  the  liver  have  separated 
from  the  blood.  The  liver  may  thus  be  ranked  with 
the  skin,  lungs,  and  kidneys,  as  an  organ  which  tends 
to  deal  with  a  certain  proportion  of  the  waste  which 
is  inseparable  from  the  wear  and  tear  of  life.  Bile 
is  a  dark  greenish-coloured  fluid  of  a  complicated 
character.  It  is,  as  we  have  seen,  a  waste  product 
made  useful.  Poured  on  the  food,  it  exerts  a  special 
digestive  action  on  the  fats  of  the  food,  breaking 
down  the  globules  of  the  fat,  emulsifying  them  and 
thus  rendering  them  more  readily  incorporated  with 
other  foods  and  also  more  readily  absorbed.  Bile 
also  exercises  on  the  food  a  certain  antiseptic  action 
preventing  the  food  in  the  intestine  from  undergoing 
injurious  changes,  whilst  a  third  function,  that  of 
stimulating  the  movements  of  the  intestine,  may  be 
attributed  to  it.  We  see  a  lack  of  this  stimulating 
action,  when,  on  account  of  the  deficiency  of  bile, 
constipation  becomes  a  marked  symptom  amongst 
other  signs  of  digestive  irregularity. 

THE  SWEETBREAD. — The  sweetbread  or  pancreas 
lies  below  and  in  front  of  the  stomach.  It  is  an 
organ  in  shape  somewhat  resembling  a  dog's  tongue, 


THE  STORY  OF  DIGESTION  51 

the  tip  of  the  tongue  lying  to  the  right  side  of  the 
body.  The  duct  or  tube  of  the  sweetbread  leads 
into  the  intestine,  and  may  join  the  duct  of  the  liver 
itself.  The  sweetbread  is  an  organ  devoted  to  the 
secretion  of  the  sweetbread  or  pancreatic  juice, 
manufactured  from  the  blood  supplied  to  the  cells  of 
the  organ.  It  is  a  clear  fluid  of  complicated  com- 
position. At  least  four  different  ferments  are 
contained  in  it.  These  are  represented  first  by  a 
substance  known  as  trypsin  which  acts  on  the  nitro- 
genous foods  so  that  any  of  these  foods  which  have 
escaped  the  action  of  the  gastric  juice  of  the 
stomach  will  be  altered  and  changed  into  peptones  in 
the  intestine.  A  second  ferment  is  that  known  as 
amylopsin,  this  substance  acting  as  does  the  ptyalin 
of  the  saliva  and  changing  starch  into  sugar.  Here, 
again,  we  meet  with  an  expedient  of  nature  whereby 
starchy  foods  which  may  have  passed  unchanged 
into  the  intestine  will  be  acted  upon  and  duly  con- 
verted into  sugar  by  the  sweetbread  secretion.  A 
third  ferment,  called  steapsin,  acts  on  fats,  and 
therefore  must  assist  the  work  of  the  bile,  whilst  a 
fourth  ferment  is  known  as  rennin,  this  last  curdling 
milk.  The  sweetbread  secretion  derives  its  impor- 
tance from  the  fact  that  it  is  the  only  digestive  fluid 
which  can  act  upon  all  kinds  of  food,  nitrogenous 
and  non-nitrogenous  alike.  Recent  researches  seem 
to  show  that  the  sweetbread  also  manufactures  what 
is  called  an  internal  secretion  not  meant  to  be 
poured  upon  the  food,  but  to  be  passed  into  the 
blood.  It  is  supposed  that  this  latter  ferment  tends 
to  destroy  or  otherwise  to  change  or  utilise  sugar 
which  has  passed  into  the  blood.  Hence  in  cases  of 
diabetes,  already  mentioned,  it  is  supposed  that 
where  this  internal  secretion  of  the  sweetbread  fails 


52 


HUMAN  PHYSIOLOGY 


to  act,  the  excess  of  sugar  in  the  blood  is  likely  to 
attain  great  dimensions  and  thus  to  constitute  a  very 
serious  phase  in  the  history  of  cases  of  diabetes. 

ABSORPTION. — We  have  now  arrived  at  the  close 
of  the  digestive  journey.  Reviewing  the  stages 
through  which  the  food  has  already  passed,  we  have 
noted  that  a  considerable  amount  of  the  nutriment 


12.— SECTION  OF  BODY 


Showing  (a)  windpipe;  (6)  junction  of  thoracic 

duct;  (c)  junction  of  right  duct  with  vein  in 

neck  ;   (d)  aorta,  or  main  descending  artery  ; 

(e  e)  lungs  ;  (/)  diaphragm  ;  (g)  kidney. 

has  already  been  conveyed  into  the  blood.  Thus 
peptones  early  left  the  stomach  and  reached  the 
blood  through  the  liver,  supplying  nitrogenous  foods 
to  the  circulation  and  thus  placing  them  quickly  at 
the  service  of  the  body.  Sugar  from  the  intestine, 
we  saw,  passes  up  the  portal  vein  and  is  dealt  with 


THE  STORY  OF  DIGESTION  53 

by  the  liver.  At  the  close  of  digestion  the  food, 
which  receives  the  name  of  chyle  (it  is  called  chyme 
when  it  leaves  the  stomach),  must  therefore  consist 
largely  of  fats,  and  this  is  found  to  be  really  the  case. 
The  chyle  is  a  fluid  resembling  milk  in  appearance. 
It  is  absorbed  from  the  intestine  by  a  delicate  series 
of  vessels  which  take  their  origin  in  little  projections 
on  the  walls  of  the  intestine  called  villi.  Passing 
through  the  cells  forming  the  outer  wall  of  these 
projections,  the  chyle  is  conveyed  by  the  absorbent 
vessels  already  mentioned  to  a  tube  termed  the 
thoracic  duct  (Fig.  12)  lying  on  the  left  side  of  the 
spine.  Received  into  this  tube,  the  chyle  is  passed 
upwards,  and  ultimately  we  find  the  thoracic  duct 
ending  in  a  large  vein  at  the  root  of  the  neck  on  the 
left  side  (Fig.  12).  At  this  point  we  may  regard  in  one 
sense  as  situated  the  junction  between  the  food  and 
the  blood.  The  absorbent  system  of  vessels,  however, 
has  other  duties  to  discharge  in  addition  to  that  of 
bringing  chyle  from  the  digestive  system  to  the  blood. 
All  through  the  body  we  find  delicate  absorbent 
vessels  termed  lymphatics  (Fig.  13).  They  are  found 
to  carry  a  clear  fluid  known  as  lymph.  This  fluid 
really  represents  colourless  blood,  and  the  lymphatics 
receive  this  lymph  as  the  overflow  of  the  blood  which 
has  escaped  from  the  finest  bloodvessels  of  the  body 
so  as  directly  to  nourish  the  most  minute  structures 
of  the  body.  As  the  absorbent  vessels  carry  this 
lymph  back  to  the  thoracic  duct  and  to  a  smaller 
and  neighbour  duct  situated  at  the  right  side  of  the 
spine  (Fig.  12),  the  ultimate  destination  of  the  lymph 
is  seen  to  be  the  blood  current,  and  into  the  blood 
stream  it  is  ultimately  poured.  The  body  is  thus 
seen  to  be  nourished  from  two  sources,  first  from 
the  food  we  eat,  and  second  from  the  lymph,  which, 


54  HUMAN  PHYSIOLOGY 

representing  the  excess  of  blood-supply,  is  gathered 
up  from  every  part  of  the  frame  and  returned  to  the 
circulation.  What  are  known  as  lymphatic  glands 
exist  in  various  parts  of  the  body,  and  are  connected 
with  the  lymphatic  system  of  vessels  or  absorbents 
as  they  are  also  called.  We  find  these  glands 
prominent  in  the  sides  of  the  neck,  in  the  arm-pits 
(Fig.  13),  in  the  groin,  and  in  other  parts  of  the 


Fig.  13. 
LYMPHATICS  OF  RIGHT  ARM. 

body.  Lymph  passes  through  them  on  its  way  back 
to  the  circulation,  the  duty  of  these  glands  being  to 
elaborate  it  and  thus  to  fit  it  more  perfectly  for 
being  added  to  the  blood  by  way  of  assisting  in  the 
repair  and  renewal  of  that  fluid. 

THE  SPLEEN.— The  spleen  situated  to  the  left 
side  of  the  stomach  may  be  regarded  as  a  "  blood 
gland,"  and  as  therefore  closely  related  in  its  nature 


THE  STORY  OF  DIGESTION  55 

to  the  lymphatic  glands  which  have  already  been 
described.  It  is  one  of  the  ductless  glands  of  the 
body,  that  is  to  say,  it  possesses  no  tube  or  duct 
issuing  from  it  like  the  liver  or  sweetbread,  and 
therefore  does  not  elaborate  any  secretion  to  be 
poured  into  the  digestive  tube  or  other  system  of 
the  body.  But  the  spleen  is  well  supplied  with 
bloodvessels.  A  very  large  artery  enters  it  and  a 
very  large  vein  leaves  it,  so  that  a  continuous 
current  of  blood  is  always  passing  through  this 
organ.  It  is  found  that  the  blood  leaving  the  spleen 
has  a  larger  number  of  white  cells  or  corpuscles 
than  the  blood  which  enters  it,  so  that  we  may 
regard  the  spleen  as  a  manufactory  of  the  white 
corpuscles  in  question.  Furthermore,  it  would  seem 
that  in  the  spleen  the  old  worn-out  red  corpuscles 
of  the  blood  are  disposed  of,  because  examination  of 
the  spleen  substance  seems  to  show  these  corpuscles 
in  all  stages  of  breakdown.  Some  authorities  are 
of  opinion  that  the  spleen  also  aids  in  the  manufac- 
ture of  red  corpuscles,  although  these  latter  are 
known  to  be  elaborated  in  other  organs  of  the  body. 
The  spleen,  it  may  be  added,  is  capable  of  being 
removed  from  the  body  of  animals  without  their 
existence  being  materially  impaired.  The  explana- 
tion is  to  be  found  in  the  idea  that,  as  the  spleen  is 
really  a  lymphatic  gland,  its  absence  is  compensated 
for  by  the  work  of  the  other  glands  of  the  system  to 
which  it  belongs. 


56  HUMAN  PHYSIOLOGY 


CHAPTER    IV 

THB    STORY    OP    THE    HEART 

THE  CIRCULATION. — In  order  that  the  nourishment 
obtained  from  the  food  should  be  duly  placed  at  the 
service  of  every  organ,  tissue,  and  cell  of  the  body, 
it  must  be  duly  circulated  through  the  frame.  This 
function  we  find  accordingly  to  be  performed 
through  the  medium  of  the  heart  as  a  central 
pumping  engine,  and  by  the  bloodvessels  or  tubes 
which  are  directly  or  indirectly  in  communication 
with  the  heart  itself.  The  blood,  as  the  common 
currency  of  the  body,  must  find  its  way  to  every 
nook  and  corner  of  the  system,  and  we  shall  note 
that  a  very  perfect  mode  of  distribution  of  the 
nutrient  fluid  is  secured  by  the  arrangements  to  be 
presently  described  as  existing  in  the  shape  of  the 
heart  and  bloodvessels.  It  is  of  importance  to  note 
in  the  first  instance  that  it  is  a  "circulation"  of 
blood  we  are  dealing  with,  and  not  a  mere  flow.  The 
difference  between  these  two  things  is  obvious.  If 
we  stand  on  the  banks  of  a  river  and  watch  the 
water  passing  us,  we  note  that  the  water  will  not 
return  again,  but  will  flow  to  the  sea  or  lake  in  which 
the  river  ends.  Circulation,  on  the  other  hand, 
implies  a  return  of  that  which  is  circulated  to  the 
starting-point,  or  at  least  includes  a  journey  or  cycle 
which  tends  in  a  sense  to  repeat  itself.  In  the  case 
of  the  distribution  of  blood  through  the  body,  the 
idea  of  a  circulation  is  really  represented;  for  if  we 


THE  STORY  OF  THE  HEART  57 

could  trace  one  blood  particle  from  any  portion  of 
the  circulation  we  should  find  that  in  course  of  time 
it  would  return  to  the  starting-point,  and  this 
circulation  would  continue  until  the  particle  was 
worn  out  or  otherwise  disposed  of.  The  meaning  of 
this  circulation  and  the  purpose  it  is  intended  to 
serve  become  clear  when  we  reflect  on  the  manner 
in  which  the  body  has  to  be  nourished,  and  the 
necessity  which  exists  for  the  waste  matter  to  be 
carried  to  the  organs  devoted  to  its  excretion  or 
removal  from  the  body.  '  Pure  blood  is  sent  out  by 
one  side  of  the  heart  (the  left)  to  nourish  the  body, 
and  is  everywhere  circulated  through  the  tissues. 
In  order,  however,  to  allow  the  outgoing  stream  of 
blood  to  reverse  its  course,  it  passes  into  vessels 
which  carry  it  away  from  all  parts  of  the  body  and 
which  end  in  the  right  side  of  the  heart.  This  latter 
side  propels  the  blood  to  the  lungs,  where  it  is  puri- 
fied. The  blood,  in  its  return  journey,  has  gathered 
impurities  and  waste  matters  from  the  tissues,  and 
it  is  these  matters  which  in  greater  part  are  excreted 
by  the  lungs,  the  skin,  and  kidneys,  the  liver,  as 
we  have  also  seen,  bearing  its  share  in  this  work. 
The  purpose  of  the  circulation  of  the  blood  may  be 
summed  up  in  the  statement  that  the  blood  so 
distributed  provides  nourishment  for  the  body,  and 
in  its  early  history  provides  material  for  growth. 
In  the  second  place  heat  is  distributed  through  the 
body  by  the  medium  of  the  blood,  whilst  in  the  third 
place  material  is  provided  to  the  various  glands  for 
the  purpose  of  enabling  them,  as  we  have  seen,  to 
manufacture  the  various  fluids  or  secretions  of  use 
in  the  body.  A  fourth  use  of  the  circulation  is  to  be 
found  in  its  acting  as  a  drainage  system,  in  that,  when 
loaded  with  waste  matters  it  is  returned  to  the  lungs 


58 


HUMAN  PHYSIOLOGY 


in  order  that  the  results  of  the  bodily  wear  and  tear 
with  which  it  has  become  encumbered  should  be 
duly  excreted. 

THE  COURSE  OF  THE  CIRCULATION. — The  course 
followed  by  the  blood  in  its  circulation  may  be  ap- 
propriately described  at  the  present  stage  of  our  en- 
quiries. Pure  blood,  returned  from  the  lungs,  enters 
the  left  auricle  (Fig.  14)  of  the  heart,  which  is  the 
smaller  and  upper  chamber  of  that  side,  the  auricle 
acting  as  a  receiver  of  the  blood. 
From  the  auricle  the  blood 
passes  directly  to  the  left  ven- 
tricle, this  last  being  the  pumping 
chamber,  and  by  the  contrac- 
tions of  this  cavity  of  the  heart 
blood  is  sent  throughout  the 
whole  body  conveyed  by  the 
arteries.  Becoming  impure  in 
the  body  the  blood  is  returned 
to  the  right  auricle  of  the  heart, 
whence  it  passes  to  the  right 
ventricle,  which  in  turn  sends 
it  to  the  lungs  for  purification. 
From  the  lungs  the  purified 
blood  passes  to  the  left  auricle, 
and  once  more  resumes  its 
circulatory  journey.  In  connec- 
tion with  the  circulation  we  have 
to  note  the  bloodvessels  or  tubes 
which  are  employed  to  distribute  blood  through  the 
body. 

ABOUT  THE  BLOODVESSELS. — The  arteries  (Fig.  14) 
are  bloodvessels  which  are  in  direct  communication 
with  the  left  side  of  the  heart,  and  into  them  the 
left  ventricle  is  perpetually  pumping  pure  blood  for 


Fig.  14.— DIAGRAM  OF 

THE  COURSE  OF  THE 

CIRCULATION 

Impure  blood  is  repre- 
sented by  the  black 
tint. 


THE  STORY  OF  THE  HEART 


59 


conveyance  over  the  body.  An  artery  is  a  vessel 
possessing  a  fairly  well  developed  coating  of 
muscular  fibres  in  its  walls.  It  is  therefore  a  more 
or  less  elastic  tube,  and  offers  little  resistance  to 
the  wave  of  blood  propelled  along  its  length  at  each 
stroke  of  the  heart.  The  muscular  coating  of  the 
artery,  serving  to  produce  the  contraction  of  the 
tube,  assists  the  work  of  the  heart,  and  it  is  the 
pulsation  which  is  set  up  by  the  wave  of  blood 
propelled  in  part  by  the  contraction  of  the  blood- 
vessels themselves  which  gives  rise  to  the  phenome- 
non known  as  the 
pulse.  A  "pulse" 
can  be  found  in 
every  artery  of 
the  body,  but  it  is 
most  definitely 
felt  at  the  wrist 
about  an  inch  or 
so  above  the  base 
of  the  thumb  on 
that  particular 
side  of  the  arm 
where  an  artery 
called  the  radial 
artery  lies  near 

the  surface  of  the  body.  To  count  the  pulse  is  of 
course  a  familiar  and  convenient  fashion  of  ascer- 
taining how  fast  the  heart  is  beating.  If  we  trace 
any  artery  sufficiently  far  in  its  course  we  find  it  to 
divide  and  sub-divide  until  we  reach  branches  so  fine 
that  they  can  only  be  seen  by  aid  of  the  microscope. 
A  very  perfect  view  of  these  finest  divisions  of 
the  arteries  called  capillaries  (Fig.  15)  can  be  ob- 
tained by  observing  the  web  of  a  frog's  foot  under 


Fig.  15.— CAPILLARIES  OF  THE  SKIN. 


60 


HUMAN  PHYSIOLOGY 


the  microscope.  These  capillaries  are  the  finest 
bloodvessels  of  the  body,  and  convey  the  blood  to 
the  most  minute  cells  and  tissues.  The  blood  itself 
passes  through  the  fine  walls  of  the  minute  blood- 
vessels, and  thus  comes  directly  in  contact  with  the 
parts  it  is  intended  to  nourish  (Fig.  16).  This  fact 
has  already  been  noted  in  the  section  dealing  with 
the  work  of  "  absorption."  The  circulation  is,  how- 
ever, continued  beyond  these  finest  bloodvessels 
onwards  into  another  and  different 
set  of  vessels  known  by  the  name 
of  veins.  Thus  arteries  end  in 
capillaries,  and  veins  begin  in 
them.  As  the  veins  leave  the 
further  parts  of  the  body  they 
tend  to  become  larger  and  larger, 
receiving  branches  in  their  course, 
and  at  last  ending  in  two  large 
vessels  which  return  blood  from 
the  lower  and  upper  parts  of  the 
body  respectively,  these  large 
veins  entering  the  right  auricle 
of  the  heart.  Another  large  vein, 
the  portal  vein,  as  we  have  seen, 
returns  blood  from  the  digestive 
organs  and  carries  it  to  the  liver 
for  purposes  already  mentioned. 
We  have  thus  three  sets  of  blood- 
vessels concerned  in  the  distribu- 
tion of  blood  through  the  body,  namely  arteries, 
capillaries,  and  veins.  The  blood  is  naturally 
pumped  by  the  force  of  the  left  side  of  the  heart 
through  the  system  of  arteries  and  capillaries,  the 
flow  of  blood  slowing  down  in  the  capillaries  just  as 
the  force  of  a  river  current  is  much  lessened  when 


Fig.   16.  —  CAPIL- 
LARIES AND  BODY 
CELLS 

The  blood  fluid 
passes  through  the 
capillary  walls  and 
nourishes  the  cells. 


THE  STORY  OP  THE  HEART  61 

the  river  begins  to  flow  out  over  level  ground  into 
a  larger  number  of  small  channels.  The  circulation 
in  the  veins,  that  is,  the  return  of  the  blood 
to  the  right  side  of  the  heart,  is  due  to  various 
causes.  There  is  first  of  all  the  force  of  the  blood 
which  is  perpetually  being  sent  out  from  the  left 
side  of  the  heart,  each  oncoming  rush  of  blood,  so  to 
speak,  forcing  onwards,  and,  in  the  case  of  the  lower 
part  of  the  body,  upwards,  in  the  veins,  the  blood 
which  has  preceded  it.  Again,  the  muscular  move- 
ments of  the  body  compressing  the  veins,  assist  the 
return  of  the  blood,  any  tendency  to  backward  flow 
being  prevented  by  the  presence  in  these  vessels  of 
pocket-like  valves.  The  mouths  of  the  pockets  open 
towards  the  heart,  so  that  whilst  blood  easily  passes 
in  that  direction,  any  back-flow  fills  the  pockets, 
which,  meeting  in  the  middle,  offer  an  obstacle  to 
regurgitation  of  the  blood. 

THE  BLOOD.— With  regard  to  the  chemical  com- 
position of  the  blood  we  find  that  it  contains  a  large 
proportion  of  water,  so  much  nitrogenous  or  proteid 
matter  held  in  solution,  this  matter  being  derived 
from  the  food,  and  a  certain  amount  of  mineral 
matter  in  addition.  Blood  when  drawn  from  the 
body  gives  us  an  idea  of  its  physical  characteristics 
and  composition,  for  it  then  separates  ultimately 
into  two  parts,  the  clot  which  falls  to  the  bottom  of 
a  vessel,  and  a  layer  of  straw-coloured  liquid  which 
rises  above.  This  liquid  is  termed  serum,  the  clot 
consisting  of  the  corpuscles  of  the  blood  which  are  en- 
tangled in  a  substance  apparently  developed  when 
the  blood  is  removed  from  the  body,  and  known  as 
"fibrin."  An  old  experiment  taught  that  if  fresh 
blood  from  an  animal  was  switched  with  willow 
twigs  it  did  not  clot.  The  reason  for  this  change  in 


62  HUMAN  PHYSIOLOGY 

the  behaviour  of  the  blood  is  explained  by  the 
fact  that  the  switching  removes  fibrin  from  the 
blood,  this  substance  being  found  in  the  shape  of 
whitish  jelly-like  threads  attached  to  the  twigs. 
Blood,  therefore,  may  be  said  to  consist  of  two  parts, 
a  fluid  part  to  which  the  name  of  plasma  is  given, 
and  solid  parts  represented  by  the  corpuscles  of  the 
blood  which  are  of  two  kinds,  red  and  white.  The 
plasma  of  the  blood  may  be  regarded  as  the  real 
blood,  for  it  contains  the  substances  which  are 
essential  for  the  nourishment  of  the  body.  The 
corpuscles,  however,  have  also  their  highly  impor- 
tant uses.  A  speck  of  blood  pressed  between  two 
thin  plates  of  glass  and  examined 
microscopically,  shows  the  clear 
plasma  of  the  blood  liquid,  whilst 
floating  in  it  are  innumerable  cor- 
puscles (Fig.  17).  Blood  may  be 
regarded  therefore  as  really  a 
clear  fluid,  seeing  that  the  blood 
Fig.  17.— BLOOD  liquor,  or  "  plasma,"  is  itself  colour- 
CORPUSCLES.  less.  It  owes  its  red  colour  to  the 
(a)  red  corpuscles  immense  number  of  red  blood  cor- 
in  rouleaux;  (c  puscles  which  float  in  the  blood 

lic*uid-     Blood  mi^ht  in  this  wav 
be  compared  to  water  in  a  ditch  in 

summer  which  appears  green  in  colour  to  the  eye. 
It  is  not  really  green,  because  if  some  of  this  water 
be  viewed  in  a  tumbler  the  clear  water  itself  is 
seen,  and  the  green  colour  is  then  perceived  to 
be  due  to  the  infinite  number  of  small  green  plants 
which  float  in  it.  So  with  the  blood;  its  colour 
is  due  to  the  immense  number  of  red  corpuscles, 
and  it  is  only  when  the  blood  is  microscopically 
treated  as  described,  that  the  eye  is  capable  of 


THE  STORY  OP  THE  HEART 


63 


perceiving  the  clear  fluid  in  which  the  corpuscles 
float. 

THE  BLOOD  CORPUSCLES. — Two  kinds  of  corpuscles , 
it  has  been  noted,  exist  in  the  blood,  the  red  and  the 
white.  The  red  (Fig  18)  are  far  more  numerous  than 
the  white,  the  proportion  on  the  average  being  1  white 
to  600  or  700  red,  although  after  meals  the  proportion 
of  white  corpuscles  appears  to  be  increased,  but  soon 
apparently  lessened  down  to  the  amount  just  stated. 
The  size  of  a  red  corpuscle  may  be  set  down  on  the 
average  at  about 
the  1 -3,200th  of  an 
inch  in  diameter; 
a  white  corpuscle 
is  somewhat  lar- 
ger, about  the 
1 -2,500th  of  an  inch 
across.  Very  im- 
portant differ- 
ences are  to  be 
noted  between  the 
white  and  red  cor- 
puscles, not  mere- 
ly in  respect  of 
their  nature,  but 
also  with  reference  to  the  duties  they  perform.  The 
red  corpuscles  contain  a  substance  called  hcemoglo- 
bin  which  contains  a  very  appreciable  amount  of 
iron.  This  substance  may  be  regarded  as  therefore 
giving  colour  to  the  blood,  and  the  value  of  iron  ad- 
ministered as  a  blood  tonic,  therefore  finds  in  the 
fact  just  related  full  justification.  The  haemoglobin 
of  the  red  blood  corpuscles  readily  combines  with 
oxygen  gas,  the  all-important  element  we  breathe  in 
from  the  atmosphere,  this  gas  being  readily  parted 


Fig.  18.— DIFFERENT  RED  BLOOD 
CORPUSCLES. 

(a)  those  of  man ;  (6)  those  of  a  frog 

oval  and  nucleated,  that  is,  having  a 

central  particle. 


64  HUMAN  PHYSIOLOGY 

with  to  the  tissues ;  for  in  the  absence  of  oxygen  no 
vital  action  can  be  performed  and  no  other  food 
utilised.  We  thus  discover  that  the  great  function 
of  the  red  blood  corpuscles  is  that  of  acting  as  the 
oxygen  carriers  of  the  blood,  so  that  this  gas  may  be 
perpetually  conveyed  to  every  tissue  of  the  body. 
The  red  blood  corpuscles  discharge  yet  another  duty. 
It  has  been  shown  that  the  blood  gathers  waste 
material  from  the  tissues,  this  waste  representing  the 
result  of  bodily  wear  and  tear.  A  part  of  this  waste 
consists  of  carbonic  acid  gas,  which,  conveyed  to  the 
lungs,  is  breathed  out.  The  red  blood  corpuscles  are 
also  carriers  of  carbonic  acid  gas  to  the  lungs,  so 
that  if  on  the  one  hand  they  act  as  distributors  of 
food  in  the  shape  of  oxygen,  on  the  other  they 
serve  as  scavengers  for  the  removal  of  waste.  The 
difference  in  colour  between  the  light  red  of  pure  or 
arterial  blood  and  the  darker  colour  of  impure  or 
venous  blood,  is  explained  by  the  fact  that  when  car- 
bonic acid  gas  unites  with  the  haemoglobin  a  darker 
hue  is  produced. 


Fig.  19.— A  WHITE  BLOOD  CORPUSCLE  OF  MAN 

SHOWING  HOW  IT  ALTERS  ITS  SHAPE. 

THE  WHITE  CORPUSCLES. — The  white  corpuscles 
are  microscopic  bodies  of  very  different  nature  from 
the  red.  Each  white  blood  corpuscle  is  in  fact  a 
living  cell,  and  as  such,  possesses  a  kind  of  semi- 
independent  existence  in  the  blood  in  which  it  lives. 
Studied  under  special  conditions  by  the  microscope, 
a  white  blood  corpuscle  is  seen  to  move  through  the 


THE  STORY  OP  THE  HEART  65 

contraction  of  the  protoplasm,  or  living  matter  of 
which  it  consists,  across  the  microscopic  field  (Fig.  19). 
If  it  comes  in  contact  with  any  solid  particle,  the  liv- 
ing body  of  the  white  blood  corpuscle  will  surround 
and  engulf  the  atom,  and  in  many  cases  will  devour  or 
dispose  of  it.  This  action  introduces  us  to  the  real 
function  of  the  millions  of  white  blood  corpuscles  con- 
tained in  the  blood  of  a  single  person.  They  may  be 
described  as  the  sanitary  police  force  of  the  body.  It 
is  known  that  when  foreign  particles,  especially  in 
the  shape  of  germs,  gain  admittance  to  the  tissues,  a 
rush  of  white  blood  corpuscles  takes  place  to  the  point 
of  infection.  They  are  capable  of  pushing  their  way 
through  the  thin  walls  of  the  finest  blood  vessels  and 
of  thus  coming  face  to  face  with  the  enemy  that  has 
literally  invaded  their  gates.  A  battle  takes  place 
between  the  invaders  and  the  defenders,  and  in  many 
cases,  though  not  in  all,  the  white  blood  corpuscles  by 
massing  together  and  bringing  their  serried  array  well 
to  the  front,  are  able  to  dispose  of  disease  germs  and 
like  particles  which  otherwise  would  tend  to  inflict 
injury  in  the  shape  of  disease  upon  the  body.  Occa- 
sionally, however,  defeat  awaits  these  wonderful  little 
defenders  of  the  living  domain.  In  the  latter  case, 
when  defeated,  they  die,  and  the  frame  thus  lies  at  the 
mercy  of  the  invading  microbes.  A  study  of  the  pro- 
cess known  as  inflammation  has  revealed  other  curi- 
ous facts  regarding  the  white  blood  corpuscles. 
When  inflammation  occurs  we  find  in  that  process,  not 
one  of  disease  as  is  commonly  supposed,  but  rather 
an  action  which  represents  the  body's  attempt  to  de- 
fend itself  against  invasion  of  disease  producing  germs. 
The  white  blood  corpuscles  or  "phagoctyes"  as 
they  are  also  called,  issue  forth  from  the  minute 
bloodvessels  in  large  numbers,  and  the  symptoms 


66  HUMAN  PHYSIOLOGY 

of  inflammation  really  represent  the  signs  of  con- 
flict which  is  being  waged  in  the  bodily  domain.  If 
the  white  corpuscles  be  defeated  and  the  inflammation, 
instead  of  being  allayed  and  subsiding,  proceeds  to 
the  length  of  suppuration,  (that  is  the  formation  of 
pus  or  matter),  we  discover  that  "  matter "  really 
consists  of  the  dead  bodies  of  the  defeated  white  cor- 
puscles. As  such  it  may  constitute,  like  the  soldiers 
left  dead  on  a  battlefield,  a  source  of  danger  to  the 
territory  around,  and  may  set  up  disease  in  other 
parts  of  the  body.  Such  is  the  history  of  the  white 
blood  corpuscles  which  practically  in  all  animals  thus 
appear  to  discharge  the  duty  of  a  sanitary  force,  ever 
on  the  alert  to  combat  invasion  of  the  body  by  disease- 
producing  particles. 

THE  HEART. — By  a  somewhat  circuitous  route  we 
have  at  last  returned  to  the  central  system  of  the  cir- 
culation, the  heart  itself.  Any  heart,  from  that  of  the 
insect  to  that  of  man,  may  be  described  as  a  hollow 
muscle.  It  is  hollow  to  receive  blood,  and  it  is  mus- 
cular that  it  may  contract  to  expel  that  fluid  in  the 
proper  directions.  There  is  thus  no  mystery  about 
the  heart  and  its  action.  The  same  form  of  energy 
by  which  we  move  our  fingers,  arms,  or  legs,  repre- 
sents the  force  which  circulates  the  nutrient  fluid 
through  our  frame.  A  glance  at  the  heart  of  a  bul- 
lock in  a  butcher's  shop  will  at  once  show  us  that  its 
substance  is  similar  to  the  animal's  flesh.  Both  are 
composed  of  muscle  with  this  difference  that  the 
heart  is  composed  of  involuntary  muscle  fibres,  that 
is,  it  acts  independently  of  the  will,  whereas  the  or- 
dinary muscles  of  arms,  legs  and  so  forth,  are  termed 
voluntary  because  they  can  be  brought  into  action 
when  we  desire  movements  to  be  performed.  At  the 
same  time,  the  heart  can  be  affected,  as  will  be  seen, 


THE  STORY  OF  THE  HEART  67 

by  and  through  the  medium  of  the  nervous  system, 
with  which  it  exists  in  very  close  and  intimate 
relationship.  A  plain  but  sufficiently  correct  idea 
of  the  heart  may  be  gained  by  comparing  it  to  two 
semi-detached  houses.  In  other  words  the  heart  is 
completely  divided  into  two  sides.  As  there  is  no 
possibility  of  the  tenant  in  one  of  the  houses 
visiting  his  neighbour  through  the  partition  wall,  so 
no  blood  can  pass  directly  from  one  side  of  the 
heart  to  the  other.  Each  side  of  the  heart,  as  we 
have  seen,  consists  of  two  chambers,  called  auricle 
and  ventricle,  and  we  have  also  noted  that  it  is  the 
duty  of  the  left  side  of  the  heart  to  propel  pure 
blood  everywhere  through  the  body,  the  function 
of  the  right  side  being  to  send  impure  blood  brought 
to  it  by  the  veins  to  the  lungs  for  purification. 
Having  regard  to  the  duties  performed  by  the  two 
sides  of  the  heart  we  see  that  the  left  side  (Fig.  21) 
has  by  far  the  greater  share  of  the  work  to  do. 
Hence,  as  might  be  expected,  the  left  heart  is  the 
much  stronger  side  of  the  two,  its  muscle  being  three 
or  four  times  the  thickness  of  that  of  the  right  side. 
THE  WORKING  OF  THE  HEART. — In  studying  the 
manner  in  which  the  heart  works  we  find  that  the 
two  auricles  contract  together,  and  the  two  ventricles 
similarly  act  in  unison.  Each  cavity  of  the  heart 
has  to  dilate  to  receive  blood,  the  auricles  from  the 
bloodvessels  pouring  blood  into  them,  and  the  ven- 
tricles from  the  auricles  themselves.  The  expansion 
or  dilatation  of  the  cavities  receives  the  name 
diastole,  whilst  when  each  cavity  of  the  heart  con- 
tracts, that  is,  grows  smaller,  it  naturally  sends  out 
its  blood;  the  act  of  contraction  being  known  as  systole. 
Returning  for  a  moment  to  the  course  of  the  circu- 
lation, *we  must  bear  in  mind  that  as  each  auricle 


68 


HUMAN  PHYSIOLOGY 


contracts  it  sends  blood  below  into  its  corresponding 
ventricle.  As  each  ventricle  contracts,  the  blood  is 
sent  out  in  the  one  case  (left)  to  the  body,  in  the 
other  case  (right)  to  the  lungs.  Having  regard  to 
these  actions  there  dawns  upon  our  minds  the 


5 


— V-    7 


3.     I 


Fig.  20.— SECTION  OF  HUMAN  HEART  (right  side). 

(7)  wall  of  right  ventricle ;  (2)  left  ventricle ;  (3)  right 
auricle  ;  (4}  appendix ;  (5  and  6)  great  veins  opening 
into  auricle  ;  (7)  aorta ;  (8)  pulmonary  artery  leading 
to  lungs  showing  valves  (10)  ;  (P)  cords  of  the  tricuspid 
valve  between  auricle  and  ventricle. 

necessity  for  some  contrivance  by  way  of  preventing 
any  reflux  or  back-flow  of  the  blood  in  the  wrong 
direction.  When  each  ventricle  contracts  to  send 
blood  to  the  lungs  or  body,  so  much  of  the  blood  if  not 


THE  STORY  OF  THE  HEART  69 

duly  prevented  might  return  into  the  auricle.  This 
reflux  is  prevented  by  the  valves  of  the  heart  (Figs. 
20  and  21)  which  constitute  one  of  the  most  in- 
teresting points  connected  with  the  structure  of  that 
remarkable  organ.  There  are  two  valves  on  each 


LV. 


Fig.  21.— LEFT  SIDE  OF  HEART  OF  MAN. 

(la)  left  auricle ;  (Iv)  thick  wall  of  left  ventricle :  (mv) 

mitral  valve ;  (pa)  pulmonary  artery,  and  (sv1)  its  valve ; 

(sy)  semilunar  valve  of  aorta  (ao). 

side  of  the  heart,  each  valve  being  more  or  less  a 
replica  of  its  neighbour  on  the  other  side.  On  the  left 
side  we  find  a  valve  between  the  auricle  and  ventricle 
called  the  mitral  or  bicuspid  valve  (Fig.  21  mv),  the 
neighbour  valve  on  the  right  side  being  called  the  tri- 
cuspid  valve  (Fig.  20,  9).  Each  of  these  valves  may 


70  HUMAN  PHYSIOLOGY 

be  described  as  consisting  of  flaps  of  the  heart's  lining 
membrane,  two  flaps  existing  on  the  left  side,  and 
three  on  the  right.  These  flaps  hang  down  into  the 
cavity  of  the  ventricle,  to  the  walls  of  which  they  are 
attached  by  thin  yet  strong  cords  (Fig.  20, 9.)  When 
blood  passes  downwards  from  the  auricle  into  the 
ventricle,  these  flaps,  falling  down,  are  pressed  closely 
against  the  walls  of  the  ventricle  and  so  allow  the  free 
downflow  of  the  blood.  When  the  ventricle  is  filled, 
the  work  of  an  instant,  the  flaps  of  the  valves  are 
floated  up  on  the  top  of  the  blood  so  that  their  edges 
meet  accurately  and  are  brought  into  perfect  apposi- 
tion (Fig.  22,  a)t  thus  forming  a  complete  partition  for 
the  time  being  between  auricle  and  ventricle.  The 
function  of  the  cords  attached  to  the  flaps  can  now 
be  understood.  As  the  blood  under  the  flaps  of  the 
ventricle  is  pressing  upwards  before  the  ventricle 
empties  itself,  these  cords  attached  to  muscular 
prominences  on  the  walls  of  the  ventricle  (Figs.  20,  P, 
and  22,  a)  pull  the  flaps  down  in  opposition  to  the  up- 
ward pressure  of  the  blood  and  thus  prevent  any 
back  flow.  When  the  blood  has  left  the  ventricle  and 
the  ventricle  dilates,  the  flaps  once  more  assume  a 
dependent  position,  and  thus  permit  of  a  fresh  flow  of 
blood  from  the  auricle  above  to  the  ventricle  below. 
The  action  of  these  valves  has  been  not  inappropri- 
ately compared  in  a  rough  way  to  the  effect  of  run- 
ning water  into  an  empty  pond.  The  leaves  of  the 
duckweed  lying  in  the  pond  are  floated  up  by  the  in- 
rush of  the  water,  and  in  a  similar  fashion  the  flaps 
or  valves  are  raised  so  as  to  constitute  a  perfect  tem- 
porary partition  between  the  two  cavities  of  the  heart. 
The  other  valves  of  the  heart  exist  at  the  entrance  to 
the  great  bloodvessels  leaving  each  ventricle.  They 
are  called  semilunar  valves  (Fig.  20,  10}  and  consist 


THE  STORY  OF  THE  HEART  71 

of  three  pockets  placed  in  a  circle  around  the  blood- 
vessel.   The  edges  of  these  pockets  being  crescentic 


Fig.  22.— DIAGRAM  OF  THE  HEART'S  ACTION. 

The  tricuspid  valve  (a)  is  shut,  and  the  semilunar  valve 
(&)  is  open  to  allow  blood  to  pass  to  lung.  The  valve  (a) 
keeps  blood  from  passing  back  into  the  auricle  (ra). 
From  the  lung  purified  blood  returns  to  the  left  auricle 
(la)  by  the  pulmonary  veins  (pv)  passes  into  the  left 
ventricle  (Iv)  and  out  to  the  body  through  the  aorta  (ad). 
(Note  the  cords  which  in  the  valve  (a)  prevent  the  flaps 
from  floating  up  into  the  auricle.) 

in  shape  have  given  rise  to  the  term  "semi-lunar"  or 
"half-moon"   shaped.    These  valves  are  somewhat 


72  HUMAN  PHYSIOLOGY 

similar  to  those  already  described  as  existing  in  veins. 
The  mouths  of  the  pockets  open  away  from  the  ventri- 
cle, and  the  passage  of  blood  from  the  ventricle  into  the 
blood  vessel  is  therefore  unfettered  (Fig.  22  6),  be- 
cause the  blood  rushes  past  the  mouths  of  the  pockets. 
If,  however,  any  back  flow  or  reflux  of  the  blood  takes 
place,  the  pockets  fill  and  their  edges  meet  in  the 
centre  and  oppose  a  barrier  to  the  regurgitation  of 
the  blood  whose  flow  they  regulate. 

THE  HEART'S  BEATS. — If  we  place  our  ear  over 
the  heart  of  an  individual  we  become  conscious,  after 
a  little  accurate  observation,  of  two  distinct  sounds. 
These  sounds  it  will  further  be  observed  show  a  cer- 
tain rhythm  in  that  they  proceed  in  pairs.    The  first 
sound  is  long  and  loud,  the  second  is  short  and  sharp. 
The  sounds  as  heard  may  be  imitated  fairly  by  pro- 
nouncing the  words  "  lubb  "  and  "  d&p."     It  is  of  great 
importance  to  note  the  meaning  of  these  sounds,  inas- 
much as  in  the  case  of  the  physician  his  power  of 
diagnosing  heart  trouble  must  depend  largely  on  his 
familiarity  with  these  sounds  in  health  and  in  disease. 
The  first  sound  appears  to  be  caused  by  the  action  of 
the  valves  between   the  ventricles,  whilst  certain 
authorities  are  of  opinion  that  the  mere  contraction 
of  the  ventricles   also   aids   in   producing   it.    The 
second  and  shorter  sound  is  undoubtedly  produced 
by  the  closure  of  the  semilunar  valves.     The  mar- 
vellous feature  connected  with  the  work  of  the  valves 
of  the  heart  is  that  of  their  instantaneous  action,  and 
moreover  in  their  perfect  working,  it  may  be,  during 
a  long  lifetime.    What  takes  even  a  limited  space  of 
time  to  describe  is  accomplished  in  the  heart  instan- 
taneously, these  valves  acting  practically  as  often  as 
the  heart  beats. 


THE  STORY  OF  THE  HEART  73 

DOES  THE  HEART  REST  ? — Oliver  Wendell  Holmes 
in  one  of  his  poems,  speaking  of  the  work  of  the  heart, 
says : — 

"  No  rest  that  throbbing  slave  may  ask, 
For  ever  quiv'ring  o'er  his  task." 

This  poetically  expressed  opinion,  that  of  an  anatom- 
ist and  physiologist  by  the  way,  is  very  far  from  the 
truth.  No  organ  of  the  body  works  perpetually. 
Even  if  its  action,  as  in  the  case  of  the  liver,  is  more 
or  less  of  a  continuous  character,  there  are  neverthe- 
less periods  during  which  the  action  is  lessened  and 
slowed  down,  and  in  this  way  a  period  of  comparative 
rest  is  represented.  In  the  case  of  the  heart  it  may 
be  said  that  it  rests  practically  as  much  as  it  works, 
its  periods  of  rest  being  equal  to  those  of  its  activity. 
It  can  be  shown  that  if  we  suppose  one  single  round 
of  the  heart's  work  to  be  represented  by  a  circle,  an 
accurate  division  of  this  circle  would  show  that  each 
interval  between  the  sounds  corresponds  exactly  to 
the  sounds  themselves  in  extent.  The  sounds  we 
have  seen  proceed  in  pairs.  The  first  sound  is 
succeeded  by  a  short  pause,  the  second  sound  next 
occurring.  A  longer  pause  exists  between  the  second 
and  the  next  first  sound  representing  the  beginning 
of  the  next  pair  of  sounds.  Measured  accurately  the 
duration  of  the  pauses  equals  the  duration  of  the 
sounds.  Rest  is  therefore  in  the  case  of  the  heart 
equal  to  work ;  only  the  heart  is  in  the  position  of  a 
workman  whose  duties  enable  him  to  take  short  spells 
of  rest  between  short  spells  of  labour.  The  amount 
of  energy  expended  in  the  circulation  of  the  blood  by 
the  heart  has  been  accurately  measured.  Knowing 
the  force  which  the  heart  exerts  in  a  single  round  of 
its  duties  it  is  a  mere  matter  of  multiplication  to  ar- 
rive at  an  estimate  of  the  amount  of  work  performed 


74  HUMAN  PHYSIOLOGY 

by  the  organ  in  say  twenty-four  hours.  This  amounts 
to  what  in  scientific  language  is  called  one  hundred 
and  twenty  foot-tons  of  work.  Put  in  plain  language 
this  statement  means  that  if  all  the  work  expended 
by  the  heart  in  twenty-four  hours  could  be  gathered 
up,  concentrated,  and  applied  to  a  huge  lift,  it  would 
raise  one  hundred  and  twenty  tons  one  foot  off  the 
ground. 

THE  HEART  AND  THE  NERVOUS  SYSTEM. — It  is  a 
familiar  fact  of  life  that  the  movements  of  the  heart 
are  influenced  by  our  emotions.  The  poet  speaks  of 
the  "  pulse  of  hope,"  and  it  is  undeniable  that  when 
an  individual  is  happy,  contented,  and  healthy,  his 
heart  beats  freely  and  with  vigour.  On  the  other 
hand,  the  play  of  a  different  emotion,  such  as  grief, 
acts  in  the  opposite  direction.  The  heart  beats  then 
become  of  a  slower  character,  and  the  circulation  is 
carried  on  less  vigorously.  The  heart  is  well  under 
the  control  of  the  nervous  system,  but  it  is  necessary, 
in  order  fully  to  appreciate  the  relations  between  the 
two  sets  of  organs,  to  remind  ourselves  that  in  addi- 
tion to  the  brain  system,  composed  of  the  brain  itself, 
the  spinal  cord,  and  the  ordinary  nerves  of  the  body, 
a  second  nervous  system  exists  in  the  shape  of  the 
sympathetic  system  which  lies  in  front  of  the  spine. 
This  latter  system  controls  actions  in  the  body  which 
are  independent  of  the  will,  and  amongst  other  duties 
it  performs,  it  is  responsible  for  controlling  the 
ordinary  work  of  the  heart.  Four  sets  of  nerves  are 
concerned  with  the  Jjeart  and  its  regulation.  Imbed- 
ded in  the  substance  of  the  heart  we  find  masses  of 
nerve  cells  belonging  to  the  sympathetic  system, 
termed  cardiac  or  heart  ganglia.  These  represent 
the  heart's  own  little  government  system,  so  that  we 
might  very  well  compare  the  organ  to  a  territory  like 


THE  STORY  OF  THE  HEART  75 

the  Isle  of  Man  which  illustrates  the  Home  Rule 
principle  in  that  it  possesses  its  own  House  of  Keys, 
regulating  its  local  affairs.  These  ganglia  are  respon- 
sible for  keeping  the  heart  duly  at  work.  The  muscle 
of  the  heart  requires  to  be  stimulated  to  action  like 
every  other  muscle  of  the  body,  and  so  we  discover 
that  the  sympathetic  system,  represented  by  these 
detached  parts  in  the  heart  substance,  will  duly  super- 
vise and  control  the  ordinary  actions  whereby  the 
the  blood  is  circulated.  Connected  with  the  heart  we 
find  a  branch  of  the  sympathetic  system  passing 
into  the  heart  and  connecting  itself  with  the  cardiac 
ganglia  just  mentioned.  Also  from  the  brain  sys- 
tem a  branch  of  a  very  large  and  important  nerve 
known  as  the  vagus  is  also  connected  with  certain  of 
the  ganglia  of  the  heart.  The  meaning  of  that  ap- 
parent dual  control  over  the  heart's  action  becomes 
clear  when,  as  the  result  of  experiment,  it  is  shown 
that  whilst  the  sympathetic  nerves  stimulate  the 
action  of  the  heart  and  quicken  it,  the  vagus  nerve 
acts  in  the  opposite  direction  and  tends  to  slow  the 
heart's  movements.  We  thus  discover  that  provision 
is  made  for  the  perfect  control  of  the  heart  in  health. 
If  circumstances  arise  when  it  is  necessary  for  the 
heart's  work  to  be  increased,  the  sympathetic  nerve 
will  effect  this  end.  If,  on  the  other  hand,  the  heart 
requires  to  be  slowed  down,  the  vagus  nerve  will  then 
come  into  play. 

THE  RELIEF  OF  THE  HEART. — So  far  a  very  com- 
plete nervous  control  is  exercised  over  the  central 
organ  of  the  circulation.  There  yet  remains,  however, 
a  fourth  nerve  which  demands  attention.  This  nerve, 
it  was  discovered,  instead  of  conveying  orders  from 
the  central  nervous  system,  carries  messages  in  the 
reverse  direction.  In  other  words,  its  purpose  is  to 


76  HUMAN  PHYSIOLOGY 

give  warning  to  a  particular  part  of  the  nervous 
system  situated  in  the  brain  of  necessary  modification 
to  be  made  in  the  heart's  labours.  Thus,  if  the  right 
side  of  the  heart  particularly  be  somewhat  fagged  in 
its  work,  and  if  heart  fatigue  begins  to  be  represented, 
a  message  passes  along  this  fourth  nerve,  to  which  the 
name  of  depressor  or  relief  nerve,  may  be  given.  The 
message  is  conveyed  to  the  nerve  centre  which  regu- 
lates the  bloodvessels,  The  result  of  what  may  be 
called  an  appeal  for  help  or  relaxation  of  its  duties 
on  the  part  of  an  overworked  heart,  received  by  this 
centre,  is  at  once  reflected  or  sent  forth  to  the  blood- 
vessels of  the  body  and  especially  to  the  large  blood- 
vessels in  the  neighbourhood  of  the  heart  itself.  The 
result  is  that  these  vessels  are  made  to  expand 
widely,  and  as  it  is  obviously  easier  for  the  heart 
to  propel  blood  through  wide  channels  than  through 
narrow  and  contracted  ones,  relief  as  in  the  case 
of  sudden  fatigue  of  the  heart  is  thus  obtained.  No 
better  example  in  the  whole  body  of  an  accurately 
acting  and  self-governing  mechanism  can  be  obtained 
than  that  just  described  whereby  the  heart  contrives 
to  gain  relief  under  conditions  of  strain  and  stress. 


THE  STORY  OF  THE  LUNGS,  SKIN  AND  KIDNEYS  77 


CHAPTER    V 

THE    STORY  OF    THE    LUNGS,    SKIN   AND   KIDNEYS 

THE  WORK  OF  THE  LUNGS. — The  function  of  breath- 
ing, or  respiration  as  it  is  also  termed,  is  discharged 
in  the  body  with  a  double  aim  in  view.  Even  a  casual 
study  of  our  breathing  movements  reveals  at  once 
the  fact  that  by  the  one  movement,  inspiration  or 
breathing  in,  we  inhale  air  from  the  atmosphere,  and 
by  the  succeeding  and  opposite  movement  of  expira- 
tion or  breathing  out,  we  exhale  air  from  the  lungs. 
A  very  casual  examination  of  the  difference  between 
the  air  breathed  in  and  that  breathed  out  further 
serves  to  show  that  the  two  movements  represent  two 
distinct  phases  of  the  work  of  the  lungs.  We  breathe 
in  atmospheric  air,  the  composition  of  which  will  be 
presently  noted,  whilst  we  breathe  out  in  addition  to 
the  air,  somewhat  altered  in  its  composition,  certain 
other  matters  representing  part  of  our  bodily  waste. 
By  inhaling  air  we  supply  the  body  with  the  oxygen 
gas,  which  has  already  been  noted  to  be  essential  for 
all  the  processes  of  life,  this  gas  being  conveyed  with 
the  pure  blood  circulated  through  the  body  to  every 
cell  of  the  frame.  On  the  other  hand  the  matters 
breathed  out  from  the  lungs  include  air  which  shows 
a  far  larger  proportion  of  carbonic  acid  gas  than  the 
air  breathed  in,  whilst  the  exhaled  air  is  found  like- 
wise to  be  loaded  with  watery  vapour  and  also  to  be 
much  warmer  than  the  air  which  is  inspired.  We 
thus  learn  in  the  first  place  regarding  the  duties  of 


78  HUMAN  PHYSIOLOGY 

the  lungs  that  whilst  inspiration  is  really  the  act  of 
feeding  the  tissues  with  oxygen,  expiration  is  an  ac- 
tion devoted  to  ridding  the  body  of  part  of  the  inevit- 
able waste  which  attends  the  continual  work  of  life. 
If  we  breathe  through  a  tube  into  a  bottle  of  lime 
water  we  find  clear  evidence  that  carbonic  acid  gas 
is  given  forth  after  each  act  of  expiration.  For  the 
water  becomes  milkier  the  longer  we  breathe  into  it, 
and  ultimately  a  white  precipitate  falls  down  in  the 
bottom  of  the  vessel,  this  substance  being  chalk.  It 
has  been  formed  by  the  addition  of  carbonic  acid  to 
the  lime  of  the  water,  chalk  being  chemically  known 
as  carbonate  of  lime.  To  demonstrate  that  the  air 
given  from  the  lungs  is  warmer  than  the  air  we 
breathe  in,  is  an  easier  matter  still.  We  have  only 
to  breathe  on  a  cold  pane  of  glass  to  notice  the  ob- 
scuring of  the  service,  whilst  such  a  simple  experi- 
ment also  proves  to  us  that  water  is  exhaled  in  the 
breath  in  the  form  of  vapour  which  condenses  on  the 
glass,  a  phenomenon  familiarly  seen  in  every  crowded 
railway  carriage,  the  windows  of  which  are  closed. 
The  function  of  breathing  has  therefore  to  be  defined 
as  a  double  one  in  which  the  nutrition  of  the  body  is 
served  in  the  first  instance,  and  the  waste  of  the  body 
partly  excreted  in  the  second. 

ABOUT  Am. — The  air  we  breathe  is  a  mixture  and 
not  a  chemical  compound  of  two  gases,  oxygen  and 
nitrogen.  Roughly  speaking  there  are  about  twenty- 
one  parts  of  oxygen  to  seventy-nine  parts  of  nitrogen 
in  a  hundred  parts  of  air.  Absolutely  pure  air  has 
this  composition,  but  ordinary  air,  which  may  for 
practical  purposes  be  regarded  as  pure,  contains  in 
addition  other  elements.  A  certain  amount  of  car- 
bonic acid  is  comprised  in  all  air  save  the  very  purest, 
but  where  the  quantity  of  this  gns  does  not  amount 


THE  STORY  OF  THE  LUNGS,  SKIN  AND  KIDNEYS  79 

to  more  than  four  parts  in  10,000  of  air,  the  purity 
of  the  air  may  be  taken  for  granted,  that  is,  having 
regard  to  its  being  safe  for  breathing.  When  on  the 
other  hand  the  quantity  of  carbonic  acid  gas  mounts 
up,  as  it  does  in  close  and  confined  places,  the  air  then 
becomes  deleterious  to  health.  In  ordinary  air  a  vari- 
able amount  of  watery  vapour  is  always  found,  and  in 
very  pure  air,  especially  that  of  the  mountain  and 
the  sea,  ozone  occurs,  this  last  being  a  very  active 
form  of  oxygen  presumed  to  have  stimulating  effects 
on  the  body,  and  therefore  credited  with  giving  to 
mountain  air  and  that  of  the  ocean,  their  invigorating 
properties.  The  air  in  addition  contains  a  certain 
amount  of  suspended  matter  in  the  form  of  invisible 
dust.  This  dust  becomes  visible  under  certain  cir- 
cumstances as  when  a  beam  of  electric  light  is  sent 
under  certain  conditions  through  air,  and  we  can 
realise  the  immense  amount  of  floating  dust  which 
ordinary  air  may  contain  when  in  a  darkened  room 
we  see  countless  motes  and  beams  dancing  in  the 
track  of  a  beam  of  sunlight  passing  in  through  a 
clink  in  the  closed  shutters.  Much  of  this  dust  con- 
sists of  mineral  matter,  but  a  certain  proportion  has 
to  be  ranked  under  the  head  of  organic  matter,  that 
is,  matter  either  itself  alive  or  derived  from  living 
bodies.  The  living  dust  of  the  atmosphere  is  repre- 
sented by  germs  or  microbes  of  various  kinds,  many 
of  them  harmless,  some  of  them  undoubtedly  disease- 
producing.  A  certain  amount  also  of  dead  material  is 
represented  in  the  air,  consisting  of  the  worn  out  cells 
and  particles  derived  from  animal  and  plant  bodies. 
It  may  be  added  that  from  the  lungs  with  each  breath 
there  is  also  expelled,  in  addition  to  heat,  water  and 
carbonic  acid,  a  certain  amount  of  organic  matter 
representing  the  worn  out  tissues  and  particles 


80  HUMAN  PHYSIOLOGY 

brought  from   all   parts  of  the   body,  and  in  part 
derived  from  the  lungs  themselves. 

VENTILATION. — One  of  the  great  problems  of  human 
life  is  to  secure  an  adequate  and  a  constant  supply  of 
pure  air.  This  task  is  much  more  difficult  than 
might  at  first  sight  be  supposed.  Our  rooms  and 
abodes  as  constructed  in  modern  times  rarely  pre- 
sent facilities  for  securing  free  and  perfect  ventila- 
tion, that  is  without  exposing  us  to  injurious  draughts 
and  so  exposing  us  to  risks  of  cold  and  chill.  The 
problem  of  ventilation  can  only  be  adequately  solved 
in  a  scientific  fashion  by  mechanical  means  whereby 
through  the  use  of  ventilating  fans  fresh  air  is 
brought  in  and  the  foul  air  expelled.  Such  means 
are,  of  course,  not  applicable  to  ordinary  dwellings, 
and  therefore  we  have  to  fall  back  in  the  latter  case 
on  simple  and  crude  expedients,  represented  by  the 
opening  of  windows  or  the  fixing  of  ventilators  which, 
however  well  they  may  act  in  theory,  rarely  come  up 
to  the  expectations  of  their  inventors  in  the  matter  of 
practice.  One  of  the  most  simple  fashions  in  which 
a  room  may  be  ventilated  at  practically  no  cost  at 
all,  is  that  of  raising  the  bottom  sash  of  a  window 
four  or  five  inches  and  of  placing  in  the  open  space  a 
bar  of  wood  on  which  the  lower  sash  rests.  The 
result  of  this  arrangement  is  to  raise  the  top  of  the 
bottom  sash  above  the  bottom  of  the  upper  sash. 
Air  comes  in  between  the  two  sashes  with  much  less 
draught  than  is  the  case  when  the  window  is  simply 
drawn  down  from  the  top.  Outlet  ventilators  may 
be  placed  near  the  ceiling,  the  ordinary  form  of  these 
ventilators  allowing  air  to  pass  out  into  the  chimney, 
whilst  the  smoke  is  prevented  by  a  valve  arrange- 
ment from  entering  the  room.  Such  ventilators,  how- 
ever, only  act  when  the  pressure  of  air  in  the  room 


THE  STORY  OF  THE  LUNGS,  SKIN  AND  KIDNEYS  81 

is  greater  than  that  represented  in  the  chimney.  The 
open  fireplace,  although  an  extremely  wasteful  appli- 
ance in  the  matter  of  coal  consumption  seeing  that 
a  very  large  proportion  of  the  heat  passes  up  the 
chimney,  nevertheless  possesses  the  advantage  of 
assisting  materially  the  ventilation  of  a  room.  A 
current  of  air  passing  up  the  chimney  displaces  so 
much  of  the  air  in  the  room  which  is  renewed  from 
the  outside,  and  thus  a  certain  circulation  of  air  is 
maintained. 

AIR  QUANTITIES. — Allusion  has  been  made  to  the 
difference  between  the  composition  of  the  air 
breathed  in  and  that  expired.  We  may  assume  that 
the  air  inspired  contains  in  one  hundred  parts  about 
twenty-one  parts  of  oxygen,  seventy-nine  parts  of 
nitrogen,  and  '04  parts  of  carbonic  acid.  On  the  other 
hand  air  which  is  breathed  out  has  naturally  its  oxygen 
diminished  owing  to  so  much  of  the  gas  having  been 
absorbed  by  the  tissues,  the  amount  being  about 
fifteen  parts.  The  quantity  of  nitrogen  does  not  alter, 
this  gas  being  inert,  and  serving  apparently  for  the 
purpose  of  diluting  the  oxygen;  whilst  the  carbonic 
acid  given  forth  is  naturally  increased  and  is  repre- 
sented by  other  four  parts  in  the  hundred  parts  of  air. 
Summing  up  the  differences  between  air  breathed  in 
and  air  breathed  out,  we  may  say  that  the  air  breathed 
in  contains  much  oxygen,  little  carbonic  acid,  a  certain 
amount  of  watery  vapour,  and  is  of  the  temperature 
of  the  surroundings.  That  which  is  exhaled  on  the 
other  hand  contains  less  oxygen,  more  carbonic  acid, 
is  of  the  temperature  of  the  blood  from  which  it  has 
passed,  this  temperature  being  98*4  degrees,  and  in 
addition  contains  a  certain  amount  of  the  organic 
matter  already  noted.  In  a  rough  way  it  may  be 
said  that  the  air  we  expire  contains  five  per  cent  less 

F 


82  HUMAN  PHYSIOLOGY 

oxygen,  and  five  per  cent  more  carbonic  acid  than 
the  air  inspired.  The  amount  of  oxygen  consumed 
in  twenty-four  hours  by  an  adult  has  been  estimated 
at  about  eighteen  cubic  feet,  this  applying  to  a  man 
at  rest.  The  amount  of  carbonic  acid  gas  given  out 
might  be  figured  forth  from  the  carbon  contained  in 
a  piece  of  charcoal  weighing  about  nine  ounces, 
whilst  the  amount  of  water  given  forth  from  the 
lungs  in  a  day  on  the  average  may  be  set  down  at 
about  half  a  pint.  Concerning  the  amount  of  air 
inhaled  at  each  breath  thirty  cubic  inches  may  be 
regarded  as  the  average  quantity  taken  in  at  each 
inspiration.  A  like  amount  will  be  given  forth  with 
the  outcoming  breath,  but  by  taking  a  deep  breath 
an  additional  hundred  cubic  inches  may  be  drawn 
into  the  lungs,  this  additional  amount  being  expelled 
along  with  the  thirty  cubic  inches  represented  as 
taken  in  by  an  ordinary  inspiration.  The  amount  in- 
haled in  quiet  breathing  (thirty  cubic  inches)  is  called 
in  scientific  language,  tidal  air,  from  the  suggestion 
that  it  represents  the  quiet  inflow  and  outflow  of  the 
tide.  The  additional  hundred  cubic  inches  taken 
in  a  deep  breath  constitute  complemental  air,  the  cor- 
responding amount  expelled  being  called  supplemental 
air.  It  must  be  noted,  however,  that  over  and  above 
the  deepest  breath  we  can  give  forth,  a  certain  amount 
of  air  remains  in  the  lungs.  This  amounts  to  about 
one  hundred  cubic  inches.  It  is  termed  residual  or 
safety  air,  for  the  reason  that  it  is  required  to 
prevent  the  chest  and  lungs  from  collapsing  through 
the  pressure  of  the  external  air. 

BREATHING  BAD  AIR. — A  great  lesson  in  public 
and  personal  health  may  be  taught  us  by  the  know- 
ledge obtained  regarding  the  necessity  for  securing 
a  supply  of  pure  air  in  order  that  our  health  and 


THE  STORY  OF  THE  LUNGS,  SKIN  AND  KIDNEYS  83 

physical  welfare  may  be  conserved.  The  story  of  the 
Black  Hole  of  Calcutta  is  familiar  to  all.  The  results 
of  breathing  and  re-breathing  foul  and  fetid  air  con- 
taminated by  the  waste  products  of  human  beings, 
received  on  that  occasion  an  object  lesson  of  histori- 
cal kind.  Other  incidents  have  occurred  to  show  the 
marked  influence  which  a  highly  polluted  atmosphere 
exercises  in  inducing  effects  of  a  serious  nature 
leading  to  ill-health,  and  in  extreme  cases  to  death. 
Whatever  difficulties  exist  in  the  way  of  procuring  fresh 
air,  it  is  at  least  something  to  realise  its  importance 
in  the  maintenance  of  health.  One  of  the  reasons 
for  the  large  amount  of  public  apathy  which  exists 
regarding  the  necessity  for  securing  a  pure  air  sup- 
ply, is  due  to  the  fact  that  the  effects  of  breathing 
polluted  air  are  generally  slow  and  insidious  in  their 
action  on  the  body.  We  rapidly  become  accustomed 
to  a  foul  atmosphere,  and  thus  fail  to  appreciate  the 
harm  which  is  being  done  by  our  inhaling  it.  The 
experiment  of  Claude  Bernard  is  well  worth  bearing 
in  mind  in  connection  with  this  topic.  He  placed  a 
sparrow  under  a  bell  jar  of  a  size  calculated  to  con- 
tain sufficient  air  to  keep  the  bird  alive  for  three 
hours.  At  the  end  of  the  second  hour  a  fresh 
sparrow  was  introduced  into  the  jar,  this  second  bird 
at  once  collapsing  and  dying  on  account  of  the  im- 
purity of  the  atmosphere  produced  by  the  first  bird, 
but  amidst  which  atmosphere  the  latter  could  live  for 
another  hour.  This  experiment,  it  is  true,  does  not 
find  its  exact  counterpart  in  humanity,  but  none  the 
less  is  the  grave  lesson  taught  us  that  a  supply  of 
pure  air  is  even  more  necessary  for  the  preservation 
of  health  than  pure  food  and  pure  water,  in  respect 
at  least,  that  we  are  always  breathing,  whilst  we  are 
not  perpetually  eating  and  drinking. 


84 


HUMAN  PHYSIOLOGY 


THE  LUNGS.— The  lungs,  two  in  number  (Fig.  23), 
are  contained  in  the  cavity  of  the  thorax  or  chest. 
This  cavity  is  bounded  by  the  spine  and  ribs  behind, 
and  by  the  breast  bone  and  cartilages  or  gristly  ends 
of  the  ribs  in  front.  It  is  a  highly  elastic  part  of  the 
skeleton,  the  elasticity  being  due  largely  to  the  pres- 
ence of  the  rib  cartilages  just  noted.  The  need  for 


Fig.  23.— THE  LUNGS  IN  POSITION  VIEWED 
FROM  THE  FRONT. 

They  rest  on  the   diaphragm   or   midriff. 
The  heart  is  shown  in  outline. 

elasticity  can  be  appreciated  when  regard  is  had  to 
the  constant  movements  the  chest  exhibits  in  the  act 
of  breathing.  The  lungs  are  suspended  freely  in  the 
chest  and  communicate  with  the  cavity  of  the  mouth 
and  with  the  air  by  means  of  the  trachea  or  windpipe 
(Fig.  24)  at  the  upper  part  of  which  we  find  situated 
the  larynx  or  organ  of  voice  (1).  The  windpipe  is 
kept  open  and  patent  by  the  pressure  of  gristly  rings 
which  can  easily  be  felt  in  the  front  of  the  throat. 


THE  STORY  OF  THE  LUNGS,  SKIN  AND  KIDNEYS  85 

Free  movement  of  the  neck  is  thus  permitted,  whilst 
the  passage  of  air  to  the  lungs  continues  uninterrup- 
tedly. The  heart  lies  between  the  lungs  (Fig.  25),  a 
situation  admirably  adapted  for  the  easy  maintenance 
of  the  close  relationship  we  have  already  noted  to 
exist  between  the  two  organs.  The  chest  is  lined 


Fig.  24 .—LARYNX  OR  VOICE  Box,  TRACHEA 
AND  BRONCHI. 

(7)  larynx;    (2)  windpipe  or  trachea;    (3} 

bronchial  tubes  or  main  divisions  of  windpipe 

in  lungs. 

and  the  lungs  covered  with  a  delicate  smooth  and 
glistening  membrane  called  the  pleura.  In  the  move- 
ments of  the  lungs  in  breathing  it  is  therefore  the 
layer  of  the  pleura  covering  the  lung  which  moves 
smoothly  on  the  layer  lining  the  chest.  A  little 
fluid  secretion  is  perpetually  thrown  out  between  the 


86 


HUMAN  PHYSIOLOGY 


two  surfaces  of  the  pleura  and  undue  friction  is  thus 
obviated.  With  regard  to  the  structure  of  a  lung  it 
may  be  described  as  a  bag  of  air  cells.  If  we  follow 
the  track  of  the  air  breathed  in  we  may  readily  be- 
come acquainted,  not  merely  with  the  actual  desti- 
nation of  the  air,  namely  the  blood  current,  but  also 
gain  at  the  same  time  a  correct  notion  of  the 
structure  of  the  lung.  The  windpipe  divides  at  the 


larynx. 


aorta 


left  lung  heort  right  lung 

Fig.  25.— THE  RELATIONS  OF  HEART  AND  LUNGS. 

root  of  the  neck  into  two  main  branches,  each  called 
a  bronchus  (Figs.  24  and  26).  The  main  division 
passes  into  the  lung  of  its  own  side  and  immediately 
begins  to  divide  and  sub-divide  into  smaller  and 
smaller  branches  which  are  known  as  bronchial  tubes 
(Fig.  26).  The  windpipe  and  bronchial  tubes  are 
lined  by  a  delicate  membrane  which  exhibits  a  special 
feature  of  its  own  in  the  fact  that  its  cells  each 


THE  STORY  OF  THE  LUNGS,  SKIN  AND  KIDNEYS  87 


possess  a  microscopic  fringe  of  lash  like  threads  of 
living  matter.  These  are  known  as  cilia.  They  are 
in  a  state  of  constant  movement  and  serve  to  waft 
up  towards  the  mouth  the  fluid  secretion  of  the  lungs, 
whilst  they  also  possess  a  certain  effect  in  clearing 
the  bronchial  tubes  of  minute  particles  which  may  be 
inhaled  in  the  air.  These  microscopic  brushes  in 


teryn* 


left  bronchiot 

Uit>e 


'powerfully 
magnified  air-ce//* 


Fig.  26.— STRUCTURE  OF  LUNGS  SHOWING  BRON- 
CHIAL TUBES  ENDING  IN  AIR  CELLS. 

other  words  possess  the  function  of  keeping  the 
bronchial  tubes  clear.  The  action  of  a  cough  can 
only  be  exercised  in  bringing  up  from  the  lungs 
matter  which  has  been  wafted  up  to  the  root  of  the 
windpipe,  and  it  is  due  to  the  action  of  these  cilia 
that  any  extra  secretion,  as  in  the  case  of  bronchitis, 
is  brought  within  reach  of  the  cough  through  the 
action  of  which  it  is  expelled  from  the  body. 


HUMAN  PHYSIOLOGY 


THE  AIR  CELLS.— Tracing  one  of  the  divisions  of 
the  windpipe  to  its  end,  we  find  that  it  ultimately  ex- 
pands into  a  clump  of  little  cells  or  compartments 
(Fig.  26)  varying  in  diameter  from  l-40th  to  l-70th  of 
an  inch.  The  end  of  the  bronchial  tube  in  this  way 
may  be  compared  to  a  passage  from  which  opens  a 
series  of  little  rooms  arranged  in  a  somewhat  circular 
fashion.  These  little  rooms  are  the  air  cells  of  the 

lung.  All  a- 
round  the  air 
cells  a  network 
of  very  fine 
bloodvessels 
exists.  These 
represent  the 
(Fig.  27)  net- 
work which  a- 
rises  from  the 
division  of  the 
bloodvessels 
coming  from 
the  right  side  of 
the  heart,  whilst 
they  also  re- 
present the  beginnings  of  the  vessels  returning  pure 
blood  to  the  heart's  left  side.  Each  little  clump  .of 
air  cells  is  in  fact  a  lung  on  its  own  account,  so  that 
when  air  is  breathed  in  and  passes  down  the  minute 
sub-divisions  of  the  windpipe  it  ultimately  arrives  at 
the  air  cells  of  the  lung,  encompassed,  as  we  have  seen, 
on  every  side,  by  bloodvessels  bringing  impure  blood 
from  the  body.  The  real  work  of  the  lung  takes  place 
in  the  air  cells,  for  according  to  a  physical  law,  that 
of  "the  diffusion  of  gases,"  the  air  breathed  in 
passes  through  the  thin  walls  of  the  air  cells  and 


Fig.  27.—THE  DENSE  NETWORK  OF 
BLOODVESSELS  IN  THE  LUNGS. 


THE  STORY  OF  THE  LUNGS,  SKIN  AND  KIDNEYS  89 

bloodvessels  into  the  blood,  while  in  the  reverse 
direction  the  carbonic  acid  gas  and  other  waste 
matters  pass  from  the  blood  into  the  air  cells  and  are 
thus  breathed  out.  This  is  the  essential  feature  of 
the  act  of  breathing,  an  interchange  of  gases  taking 
place  in  the  air  cells  of  the  lung.  The  lung  might  in 
fact  be  well  compared  to  a  market  place  or  exchange 
where  business  is  conducted  by  two  merchants 
represented  by  the  air  and  blood  respectively.  The 
transaction  is  one  of  barter,  the  air  proposing  to 
give  to  the  blood  its  oxygen,  whilst  the  blood 
exchanges  for  this  necessary  item,  carbonic  acid  gas, 
heat  and  water,  which  are  given  forth  in  expiration. 
How  WE  BREATHE. — The  one  movement  of  breath- 
ing, inspiration,  differs  very  materially  in  its  nature 
from  its  neighbour,  that  of  expiration.  We  may  de- 
termine this  fact  if  we  pay  attention  to  our  own 
breathing  movements.  Breathing  in  is  essentially  a 
muscular  act  which  chiefly  depends  on  the  action  of 
a  very  large  muscle  forming  a  moveable  floor  to  the 
chest,  this  muscle  being  known  as  the  diaphragm  or 
midriff  (Fig-  23).  This  muscle,  when  it  acts,  descends 
and  becomes  less  convex  in  shape,  with  the  result, 
that  on  account  of  its  attachment  to  the  chest  walls 
it  enlarges  that  cavity,  making  it  broader  and  longer. 
At  the  same  time  the  breast  bone  is  pushed  forward 
and  upward  chiefly  by  the  action  of  the  little  mftecles 
which  exist  between  the  ribs,  so  that  the  chest  in  this 
way  is  also  enlarged  in  depth.  The  lungs,  which  are 
highly  elastic  bodies,  follow  every  movement  of  the 
chest,  hence,  pressed  as  they  have  been  to  a  certain 
degree  before  the  act  of  inspiration  begins,  they  ex- 
pand in  virture  of  their  elasticity,  and  thus  admit  the 
supply  of  air  which  is  drawn  in  by  the  act  of  inspir- 
ation. When  this  action  comes  to  an  end,  it  is 


90  HUMAN  PHYSIOLOGY 

exchanged  for  that  of  breathing  out.  Here  we  come 
face  to  face  with  an  act  which  is  largely  mechanical 
in  its  nature,  and  does  not  involve  muscular  action, 
In  breathing  out  we  simply  see  the  recoil  of  the  chest, 
and  the  return  of  the  elastic  structures  to  their  posi- 
tion of  rest  from  which  they  were  disturbed  by  the 
act  of  breathing  in.  Inspiration,  therefore,  is  the 
one  act  which  involves  an  expenditure  of  muscular 
energy,  while  breathing  out  as  a  mechanical  act 
makes  no  demands  upon  our  working  power.  Nature 
in  this  respect  supplies  an  example  which  might  be 
paralleled  by  many  other  instances,  of  an  economical 
use  of  her  working  powers. 

THE  SKIN. — The  lungs  do  not  stand  alone  in  the 
category  of  our  bodily  belongings.  As  a  matter  of 
fact  they  represent  one  of  a  number  of  organs  per- 
forming the  same  work  although  the  labour  is  carried 
out  in  different  fashions.  The  neighbour  organs  of 
the  lungs  are  the  skin  and  kidneys,  so  that  the  three 
form  a  kind  of  physiological  trio  whose  action  is  that 
of  excreting  waste  matter  from  the  body,  the  lungs 
acting  in  a  highly  important  fashion  because  they  like- 
wise perform  the  function  of  absorbing  oxygen.  The 
functions  of  the  skin  are  of  a  varied  character.  In 
addition  to  serving  as  a  body-covering,  the  nerves  of 
its  under  layer  supply  us  with  the  means  of  exercis- 
ing the  sense  of  touch.  The  glands  of  the  skin  con- 
stitute it  an  organ  of  excretion  for  the  getting  rid  of 
waste  matter,  whilst  the  large  supply  of  blood  con- 
tained in  these  minute  bloodvessels  renders  the  skin 
an  organ  which  regulates  to  a  large  degree  the  tem- 
perature of  the  body.  These  varied  functions  being 
borne  in  mind  teach  us  that  the  skin  is  really  an  ex- 
tremely complex  structure,  and  in  respect  of  its  func- 
tions it  may  be  described  legitimately  as  a  kind  of  lung 


THE  STORY  OP  THE  LUNGS,  SKIN  AND  KIDNEYS  91 

spread  over  the  surface  of  the  body.  In  its  structure 
the  skin  exhibits  a  main  division  into  two  layers.  The 
outer  coating  is  the  epidermis  or  scarf  skin,  which 
possesses  neither  nerves  nor  bloodvessels  and  con- 
sists of  cells  perpetually  renewed  from  the  upper  sur- 
face of  the  under  skin.  The  dermis  or  under  skin, 
lying  below  the  outer  layer,  contains  both  nerves  and 
bloodvessels,  the  ends  of  the  nerves  being  contained 
within  little  projections  of  this  under  layer  known  as 
papillcs.  Below  this  under  layer  of  the  skin  we  come 
upon  other  tissues  including  fat. 

THE  GLANDS  OF  THE  SKIN. — The  glands  of  the 
skin  are  two  in  number.  The  sebaceous  glands 
are  small  pocket-like  organs,  the  ducts  or  tubes  of 
which  open  into  the  sheaths  of  the  hairs  and  also 
frequently  pass  to  the  surface  of  the  skin  itself. 
These  glands  secrete  an  oily  or  fatty  material, 
the  function  of  which  is  to  keep  the  skin  pliant 
and  moist,  whilst  from  their  relation  to  the 
hairs  it  may  be  assumed  that  their  secretion  may 
also  be  held  to  represent  a  natural  oil  or  pomade. 
More  important  are  the  sweat  glands  whose 
action  it  is  to  separate  from  the  fine  bloodvessels 
surrounding  them  certain  waste  products  constitut- 
ing the  sweat.  The  sweat  consists  of  a  large  amount 
of  water,  minerals  (amongst  which  common  salt  is 
prominent),  and  certain  fatty  matters  derived  from 
the  skin's  surface.  A  certain  amount  of  carbonic 
acid  gas  is  also  given  forth  from  the  skin,  whilst  most 
physiologists  agree  that  the  skin  has  a  limited  power 
of  absorbing  oxygen.  The  sweat  glands  consist  each 
of  a  minute  coiled  up  tube,  the  end  of  which  passes 
upwards  to  the  skin  and  opens  in  a.  pore.  The  coiled 
up  part  of  the  tube  especially  is  lined  by  cells,  which 
are  the  active  agents  in  taking  from  the  blood  the 


92  HUMAN  PHYSIOLOGY 

waste  matters  which  the  gland  passes  upwards  to  the 
skin  surface.  Sweat  glands  are  most  numerous  in 
the  palm  of  the  hand  and  sole  of  the  foot,  the  num- 
ber in  these  regions  being  estimated  at  about  3,000 
per  square  inch.  In  the  neck  and  back  they  are  less 
numerous.  It  has  been  estimated  that  over  two 
millions  of  these  glands  exist  in  the  skin  surface  of  a 
human  body.  If  the  coiled  up  tube  was  stretched 
out  at  full  length  it  would  measure  about  a  quarter 
of  an  inch,  so  that  according  to  one  estimate,  in  a 
square  inch  of  skin  from  the  palm  of  the  hand  the 
length  of  the  sweat  tubing  would  be  found  to  be  over 
seventy-three  feet.  The  total  length  of  sweat  tubing 
in  the  body  has  been  variously  given  as  amounting 
to  ten  miles,  some  estimates  vastly  exceeding  this 
calculation. 

THE  SKIN  ACTION. — The  skin  glands  are  always 
acting,  and  hence  perspiration  which  is  poured  forth 
under  circumstances  of  quietude  of  the  body  is 
termed  insensible  perspiration.  After  exertion,  when 
the  sweat  may  become  visible  on  the  surface  of  the 
skin,  it  is  then  known  as  sensible  perspiration.  The 
amount  of  sweat  given  off  on  an  average  from  the 
body  of  a  man  per  day  is  about  two  pounds,  an 
amount  liable  to  be  vastly  increased  where  violent 
exercise  or  heavy  work  is  represented. 

THE  SKIN  AND  BODILY  HEAT. — In  order  to  appre- 
ciate the  duty  of  the  skin  as  a  regulator  of  the 
temperature  or  heat  of  the  body,  we  have  first  of  all 
to  remember  the  vast  amount  of  blood  which  is 
perpetually  circulating  through  the  skin  in  its  minute 
bloodvessels  or  capillaries.  These  bloodvessels  are 
under  the  control  of  the  nervous  system,  and  are 
maintained  in  a  medium  state  which  may  be  described 
as  that  between  contraction  and  expansion.  If, 


THE  STORY  OF  THE  LUNGS,  SKIN  AND  KIDNEYS  93 

however,    from    any    circumstances    the    nervous 
control  is  lessened,  the  bloodvessels  dilate  or  expand, 
with  the  result  that  a  greater  flow  of  blood  passes 
through  them  and  greater  activity  of   the  sweat 
glands  is  produced.    A  warm  bath  produces  this 
effect.     It  relaxes  the  skin  and  bloodvessels,  brings 
more  blood  to  the  skin  surface,  and  this  favours 
perspiration.    Cold  acts  in  a  reverse  fashion  and 
diminishes  the  supply  of  blood,  lessening  at  the  same 
time  the  amount  of  perspiration  given  off.     Some- 
thing of  this  skin  regulation  of  temperature  and  the 
resulting  alteration  produced  in  its  work  may  be 
appreciated  in  the  difference  between  the  work  of 
the  kidneys  and  skin  in  summer  and  in  winter.     In 
summer  when  the  skin  acts  freely,  the  work  of 
the  kidneys  is  lessened,  whereas  in  cold  weather  skin- 
action  is  apt  to  be  in  some  degree  checked  and  the 
kidneys  excrete  more  fully.     It  is  the  evaporation  of 
perspiration  from  the  skin  surface  that  aids  largely 
in  the  regulation  of  temperature.    The  sweat,  as  a 
fluid,  evaporates  and  passes  off  into  the  air,  and  thus 
removes  a  certain  amount  of  heat  from  the  body 
with  the  result  of  cooling  the  body  at  large.    On  the 
other  hand,  when  the  atmosphere  is  cold,  less  sweat 
being  produced,  the  loss  of  heat  from  the  body  is 
lessened;  and  so  under  the  varying  circumstances 
of  life  and  under  varying  degrees  of  temperature 
the  bodily  heat  is  regulated  and  maintained  at  very 
much  the  same  degree — 98.4  degrees  F. 

THE  CARE  OF  THE  SKIN. — Of  the  most  extreme 
importance  to  health  is  the  care  of  the  skin.  Recog- 
nising the  elaborate  functions  it  performs,  we  are 
taught  our  duty  to  the  skin  in  maintaining  its  cleanli- 
ness and  in  encouraging  its  work.  Interference  with 
the  functions  of  the  skin  may  be  productive  of  very 


94  HUMAN  PHYSIOLOGY 

serious  results,  a  sudden  checking  of  these  functions 
reacting  upon  the  internal  organs  of  the  body  and 
producing  congestion  which  is  the  first  stage  of 
inflammation,  thus  giving  rise  to  cold  and  lung 
troubles  at  large.  Again,  any  material  interference 
with  the  free  excretion  of  perspiration  may  have  a 
fatal  result.  In  a  Papal  procession  at  Rome,  the 
body  of  a  child  was  covered  over  with  gold  leaf  to 
represent  a  figure  in  the  pageant  of  the  Golden  Age. 
The  child  died  in  a  few  hours  from  a  veritable 
process  of  suffocation  due  to  the  retention  within 
the  body  of  the  waste  products  naturally  secreted 
by  the  skin.  The  proper  use  of  baths,  and  the  main- 
tenance of  the  skin  in  a  state  of  high  cleanliness  is 
therefore  one  of  the  duties  we  owe  to  ourselves  when 
the  care  of  our  health  falls  to  be  considered. 

THE  KIDNEYS. — The  interdependence  of  the  lungs, 
skin  and  kidneys  may  be  demonstrated  in  yet  another 
fashion  apart  from  that  which  teaches  that  the  three 
organs  perform  very  much  the  same  kind  of  work. 
Where  the  lungs  are  affected,  part  of  the  rational 
medical  treatment  of  lung  troubles  is  to  increase  the 
action  of  the  skin  by  administering  medicines  which 
cause  profuse  perspiration;  and  the  same  is  true 
when  the  kidneys  are  affected.  One  organ  is  thus 
capable  to  a  certain  extent  of  relieving  the  others  in 
their  work.  The  kidneys  are  two  in  number,  one  on 
each  side  of  the  lumbar  or  loins  region  of  the  body. 
The  term  "kidney-shaped"  is  a  familiar  enough 
expression,  and  serves  to  indicate  the  form  of  the 
kidney  which  is  convex  to  the  outer  side  and  deeply 
indented  on  the  inner  side.  A  very  large  artery,  the 
renal  artery,  given  off  from  the  aorta,  enters  each 
kidney,  and  a  very  large  vein,  the  renal  vein,  joining 
the  vena  cava,  leaves  it  (Fig  28).  The  blood  leaving 


THE  STORY  OF  THE  LUNGS,  SKIN  AND  KIDNEYS  95 

the  kidneys  is  the  purest  blood  in  the  body,  but  of 
course  it  soon  mixes  with  the  general  venous  stream 
from  the  body  at  large,  passing  back  to  the  lungs 
by  the  vena  cava  (Fig.  28)  for  purification.  There 
is  thus  a  perpetual  flow  of  blood  through  the 
kidney,  and  although  it  is  pure  blood  which  enters 
by  the  artery,  such  blood  nevertheless  contains 


Fig.  28. — THE  KIDNEYS  IN  POSITION. 

(1  and  2)  kidneys,  (3)  vena  cava,  (4)  aorta,  (5,  5) 

ureters  leading  to  bladder. 

certain  of  those  products  which,  resulting  from 
the  breakdown  in  the  body  of  the  nitrogenous  foods, 
are  destined  to  be  removed  from  the  blood 
by  the  organs  we  are  considering.  The  structure 
of  the  kidney  is  somewhat  of  a  complicated  nature. 
The  essential  feature  of  the  organ  consists  in  the 
presence  of  a  large  number  of  little  bodies,  each 
containing  a  ball  or  network  of  fine  capillaries  which 


96  HUMAN  PHYSIOLOGY 

represent  the  end  of  the  renal  artery  and  the  begin- 
ning of  the  renal  vein.    The  blood  which,  so  to 
speak,  circulates  in  and  out  of  the  kidney,  finds  its 
turning  point  in  the  little  bodies  (Malpighian  bodies) 
just  noted.    These  structures  are  lined  by  cells  which 
represent  the  active  agents  in  the  kidney's  work. 
The  little  artery  entering  the  Malpighian  body  is 
wider  in  diameter  than  the  vein  which  is  given  off, 
hence  the  blood  is  forced  at  a  certain  pressure  into 
these  bodies,  and  in  this  mechanical  fashion  the  waste 
matters  are  excreted,  especially  water,  which  forms 
the  great  bulk  of  the  kidney  secretion  or  urine. 
Each  of  the  Malpighian  bodies  is  in  fact  a  kind  of 
filter  which  filters  out  from  the  blood  the  waste 
matters  of  the  kidney  secretion.     From  each  of  these 
bodies  a  tube  passes  out  in  a  varied  and  somewhat 
complicated  arrangement  to  the  centre  of  the  kidney, 
the  multitude  of  tubes  ending  in  the  hollow  of  the 
kidney  on  certain  little  projections  or  papilla.    It 
would  seem  that  the  fluid  part  of  the  urine  or  water 
is  really  forced  from  the  blood  by  a  process  of 
filtration  within  the  little  bodies  described,  whilst 
the  other  matters  removed  from  the  blood  are  in  all 
probability  separated  by  the  cells  of  the  Malpighian 
bodies  themselves,  and  by  those  which  line  the  tubes 
leading  from   the   bodies  in    question    and    which 
conduct  the  urine  to  the  outlet  of  the  kidney.     From 
each  kidney  a  special  tube,  the  ureter,  leads  to  the 
bladder  in  which  the  urine  is  stored  preparatory  to 
its  expulsion. 

THE  KIDNEY  SECRETION. — A  healthy  adult  will 
pass  from  the  kidneys  in  twenty-four  hours  between 
fifty  and  sixty  fluid  ounces  of  urine,  although  the 
quantity  varies  materially  according  to  the  circum- 
stances of  life,  and  even  according  to  the  outer 


*f  HE  STORY  OP  THE  LUNGS,  SKIN  AND  KIDNEYS  9? 

temperature.  The  urine  consists  in  1000  parts,  of 
about  958  parts  of  water  and  42  parts  of  solids,  the 
latter  consisting  of  urea,  uric  acid,  minerals  and 
other  substances,  whilst  a  certain  amount  of  carbonic 
acid  gas  has  also  to  be  reckoned  with  as  being 
contained  in  the  urine.  The  special  feature  we  have 
to  remember  in  connection  with  the  functions  of  the 
kidneys  relate  to  the  urea  and  the  uric  acid.  Both 
substances  represent  what  we  may  term  the  break- 
down of  the  nitrogenous  foods  consumed  and  utilised 
by  the  body.  The  uric  acid,  in  the  opinion  of  many 
physiologists,  represents  a  stage  in  advance  of  that 
which  results  in  the  production  of  urea.  As  an 
excess  of  uric  acid  in  the  body  is  the  cause  of  gout, 
that  disease  may  be  presumed  to  arise  from  some 
condition  or  other  which  prevents  the  work  of  the 
kidney  being  carried  on  to  its  normal  end. 

A  BODILY  BALANCE  SHEET. — It  is  now  possible  to 
summarise  in  the  form  of  a  bodily  balance  sheet  the 
general  income  and  expenditure  of  the  living  body, 
the  details  of  which  have  hitherto  formed  the  subject 
of  our  studies.  In  this  fashion  we  may  gain  a 
summarised  idea  of  the  manner  in  which  the 
business  of  life  is  conducted,  and  we  may  also  be 
prepared  to  discover  that  in  respect  of  economical 
working,  nature  presents  a  highly  typical  example  of 
the  wise  and  orderly  ruling  in  her  conduct  of  the 
human  household.  The  total  income  of  a  human 
being  is  derived  from  three  sources,  namely,  the  solid 
food  he  consumes,  the  water  or  other  fluids  he  drinks, 
and  the  oxygen  of  the  air  he  inhales.  The  expendi- 
ture of  his  body  is  represented  by  the  waste  materials 
which  have  resulted  from  the  work  his  body  performs. 
The  income  of  an  adult  man  doing  an  ordinary  amount 
of  work  per  day  may  be  calculated  as  nearly  as  possible 


98  HUMAN  PHYSIOLOGY 

to  amount  to  8,000  grains  of  solid  food,  37,650  grains 
of  water,  and  13,000  grains  of  oxygen,  making  up  a 
total  of  about  8£  pounds  of  material  by  weight.  His 
expenditure  from  the  lungs  of  the  waste  matter 
given  forth  will  amount  to  20,000  grains,  the  skin 
giving  off  11,750  grains,  the  kidneys  24,100  grains, 
the  intestines  2,800  grains  of  waste  digestive  matter. 
The  expenditure,  amounting  to  about  8$-  pounds, 
would  be  found  to  balance  the  income.  It  is 
impossible  for  us  of  course  to  obtain  mathematical 
exactitude  when  dealing  with  living  beings,  but  the 
figures  just  given  offer  as  near  an  approach  as  is 
possible  to  the  real  facts  of  the  case. 

OUR  BODILY  PROFIT. — Here  arises  an  extremely 
interesting  question,  namely,  that  regarding  the  profit 
which  is  derived  from  this  apparant  exact  balancing 
of  the  income  and  expenditure.  Unless  the  business 
of  life  is  conducted  on  lines  widely  different  from 
those  on  which  the  commercial  transactions  of  men 
are  founded,  it  is  clear  the  business  of  living  must  in 
one  sense  be  regarded  as  highly  unprofitable,  and  as 
showing  nothing  which  may  be  reckoned  in  the  light 
of  gain.  This  conception,  however,  is  extremely 
erroneous,  for  the  profit  derived  out  of  the  business 
transactions  of  life  really  represents  an  enormous 
gain.  The  profit  we  obtain,  summed  up  in  a  single 
word,  is  "the  power  of  doing  work."  Whatever 
work  man  performs  in  the  world,  his  ability  to 
exercise  bone,  muscle,  and  brain,  is  derived  from  the 
transaction  just  chronicled.  The  case  of  the  engine 
we  may  again  recall  to  mind  by  the  statement  of  the 
bodily  balance  sheet.  The  profit  represented  by  the 
work  of  the  engine  is  found  in  the  power  which  it 
develops  out  of  the  fuel  supplied  to  it.  Now  in 
respect  of  man's  inventions  this  profit  is  by  no 


THE  STORY  OF  THE  LUNGS,  SKIN  AND  KIDNEYS  99 

means  large.  Even  the  best  constructed  machine 
will  only  give  a  very  limited  percentage  of  power 
when  compared  with  the  amount  of  fuel  it  consumes. 
The  case  is  extremely  different  with  the  human 
engine,  for  on  a  comparatively  small  amount  of  fuel 
it  gives  an  amount  of  energy  which  is  positively 
startling  when  we  come  to  sum  up  the  various  items 
whereof  it  is  composed.  If  we  calculated  the  power 
developed  by  the  body  as  a  living  engine  out  of  the 
food  it  consumes,  we  find  that  according  to  one  calcu- 
lation, the  internal  work,  that  of  maintaining  the  body 
itself,  may  be  reckoned  as  equal  to  2,800  foot  tons 
per  day — that  is  to  say,  if  applied  in  the  shape  of 
mechanical  work,  this  amount  of  energy  would  be 
capable  of  raising  2,800  tons  one  foot  from  the 
ground.  The  same  estimate  maintains  that  an 
ordinary  day's  work,  about  300  foot  tons,  will 
really  be  increased  five  times,  namely,  1,500  foot  tons, 
in  addition  to  the  quantity  required  for  the  body's 
own  maintenance.  Thus  we  get  1,500  foot  tons  plus 
2,800,  or  4,300  foot  tons  in  all,  developed  from  the 
fuel  supplied  to  us  in  the  shape  of  our  food.  This 
tremendous  amount  of  working  power  represents  the 
profit  we  obtain  from  the  transactions  we  carry  out 
every  day,  in  the  way  of  obtaining  our  food,  and  of 
assimilating  it  and  digesting  it.  If  the  amount  of 
power  expended  in  the  work  we  perform  daily,  apart 
from  the  internal  work  of  the  body,  be  calculated,  a 
man  at  light  work  develops  from  150  to  200  foot  tons 
per  day.  The  average  work  is  estimated  at  from 
300  to  350  foot  tons  in  the  case  of  a  hard  worker. 
In  the  case  of  a  hard  worker  he  may  develop  between 
450  and  500  foot  tons,  and  in  laborious  work  between 
500  and  600  foot  tons.  Another  mode  of  calculation 
teaches  us  that  out  of  his  daily  food  a  man  requires 


100  HUMAN  PHYSIOLOGY 

to  renew  daily  his  store  of  energy  equal  to  a 
mechanical  work  which  would  lift  nearly  1  ton  a 
height  of  1,094  yards.  Differ  as  the  estimates  may 
regarding  man's  working  profit  derived  from  his 
food  consumption,  we  are  at  least  standing  on  sure 
ground  when  we  assert  that  the  profit  he  exhibits  as 
a  working  engine,  in  the  shape  of  energy,  far  exceeds 
that  ever  likely  to  be  developed  by  any  of  his  own 
inventions. 


THE  STORY  OF  THE  BRAIN  AND  NERVE      101 


CHAPTER  VI 

THE  STORY  OF  THE  BRAIN  AND  NERVE 

THE  Two  NERVOUS  SYSTEMS. — The  control  of  a 
living  body,  like  the  government  of  a  country,  is 
found  to  be  determined  by  a  specially  appointed 
organisation  to  which  we  apply  the  general  name  of 
the  nervous  system.  This  system,  whilst  exhibiting 
a  distinct  unity,  is  nevertheless  composed  of  elements 
or  parts  of  diverse  importance,  some  being  of  vastly 
greater  importance  than  others,  judged  by  the  special 
share  of  the  work  of  government  they  perform. 
Two  nervous  systems  exist  in  the  bodies  of  all  back- 
boned animals,  a  fact  already  alluded  to  when  we 
dealt  with  the  general  constitution  of  the  body.  The 
more  important  of  these  two  systems  consists  of  the 
brain  and  spinal  cord  (Fig.  29  and  30),  which  last  may 
be  described  as  the  main  line  of  the  nervous  system, 
lying  protected  within  the  spine,  and  the  nerves  issu- 
ing from  both  brain  and  cord  supplying  the  body  with 
the  means  of  communication  between  itself  and  the 
outer  world.  The  second  system,  known  as  the 
sympathetic  system,  exists  in  the  form  of  a  double 
chain  of  ganglia  or  masses  of  nerve  cells  lying  in  front 
of  the  spine.  This  latter  system  has  an  individuality 
of  its  own,  though  it  is  connected  at  certain  points 
with  the  brain  system  of  nerves.  The  term  cerebro- 
spinal  system  is  scientifically  applied  to  the  latter  in 
contra-distinction  to  the  term  sympathetic,  denoting 
the  other  main  portion  of  the  nervous  apparatus.  In 


102 


HUMAN  PHYSIOLOGY 


the  presence  of  these  two  nervous  systems,  we  come 
face  to  face  with  what  may  be  termed  the  principle 
of  the  division  of  labour  as  re- 
presented in  the  government  of 
the  body.  The  brain  system  exer- 
cises all  those  functions  which  are 
especially  associated  with  volun- 
tary movements  and  the  exercise 
of  the  will.  The  power,  in  other 
words,  of  doing  as  we  like,  depends 
upon  our  possession  of  this  nervous 
system  whereby  the  commands 
which  the  brain  sends  forth  are 
capable  of  being  executed  by  the 
body  at  large,  whilst  in  the  same 
way,  information  conveyed  by  the 
senses  from  the  outer  world  to 
the  brain  can  be  appreciated,  and, 
if  necessary,  acted  upon  by  the 
body.  The  sympathetic  system, 
on  the  other  hand,  may  be  de- 
scribed as  the  "  involuntary"  nerv- 
ous system.  It  cannot  be  directly 
brought  into  play  by  the  exercise 
of  the  will,  but  can  only  be  stimu- 
lated indirectly,  as,  for  example, 
when  we  take  food  into  the 
stomach,  the  movements  of  the 
organ,  regulated  by  the  nervous 
Fig.  29.  system,  being  thus  stimulated. 

SPINAL  CoRAi^  Actions,  of  which  a  very  consider- 
THE  CEREBRO-  able  number  are  performed  by  the 
SPINAL  SYSTEM.  body>  such  as  are  more  or  less 

of  automatic  or  machine-like  character,  are  regulated 
and  supervised  by  the  sympathetic  system.     For 


THE  STORY  OF  THE  BRAIN  AND  NERVE     103 


example,  the  heart  and 
bloodvessels  are  con- 
trolled by  this  system, 
and  the  movements  of 
the  intestine  in  diges- 
tion, depend  for  their 
control  upon  the  sym- 
pathetic nerves.  The 
division  of  labour  prin- 
ciple is,  therefore,  seen 
to  be  illustrated  in  the 
work  of  the  two  nervous 
systems,  seeing  that  a 
vast  number  of  impor- 
tant actions  upon  the 
due  performance  of 
which  existence  itself 
may  be  said  to  depend, 
are  regulated  not  by  us, 
but  for  us.  The  work  of 
the  sympathetic  centre 
consists  in  supervising 
what  may  be  called  the 
ordinary  actions  of  the 
body  connected  with 
digestion,  circulation, 
and  the  like,  while  the 
brain  system  remains 
free  for  the  supervision 
of  the  more  important 
questions  and  actions  of 
the  day  and  the  hour. 

WHAT  THE  NERVOUS 
SYSTEM  DOES. — 
If  a  broad  but 


•ig.   3u.  —  VIEW   OF    SPINAL 
CORD,  SHOWING  ITS  CONNEC- 
TION WITH  THE  BRAIN,  AND 
THE  SPINAL  NERVES  ISSUING 
FROM  THE  CORD. 


104  HUMAN  PHYSIOLOGY 

comprehensive  view  be  taken  of  the  functions  of 
any  nervous  system,  whether  in  lower  or  in  higher 
/forms,  we  might  define  it  as  a  particular  series  of 
j  organs  in  an  animal  body  set  apart  for  the  purpose 
\of  exercising  the  function  of  Relation.  By  this  latter 
term  is  implied  the  bringing  of  the  living  being  into 
"  relation  "  with  the  world  in  which  it  lives.  Apart 
from  the  possession  of  a  nervous  system  or  its 
equivalent  in  the  lowest  forms,  the  living  being 
would  be  incapable  of  reacting  upon  the  impressions 
received  from  the  outer  world.  It  would,  in  other 
words,  be  a  non-sensitive  thing,  and  it  might,  there- 
fore, take  rank  with  inorganic  or  non-living  objects. 
All  living  things  may  be  regarded  as  possessing  a 
definite  amount  of  sensitiveness,  and  this  opinion 
holds  good  for  the  lowest  animals,  and  also  for 
plants  in  which  no  trace  of  nervous  system  has  as 
yet  been  discovered.  But  as  living  matter  itself  is 
everywhere  sensitive,  we  can  understand  that  in  the 
absence  of  a  nervous  apparatus,  a  small  speck  of 
living  matter  constituting  the  body  of  a  lower 
animal,  exercises  the  function  of  sensation,  is  able  to 
feel  the  contact  of  food  particles,  and  to  act  upon 
the  impressions  to  which  the  contact  with  these 
particles  gives  rise.  From  this  view  of  the 
nervous  system  we  may  advance  to  yet  another 
generalisation  of  some  service  in  enabling  us  to 
understand  the  difference  between  a  nervous  system 
of  low  degree  and  one  of  high  degree.  The  higher 
nervous  system  of  animals  possesses  a  more  perfect 
and  intimate  relationship  developed  between  its 
possessor  and  the  world  in  which  it  lives.  Take,  for 
example,  the  acts  of  a  highly  organised  brain  and 
nervous  system  which  a  dog  posesses.  It  is  capable 
of  exercising  a  high  degree  of  intelligence,  yet  it  falls 


THE  STORY  OF  THE  BRAIN  AND  NERVE      105 

marvellously  short  of  human  acquirements,  even  in 
respect  of  those  traits  which  mark  a  simple  mental 
or  nervous  operation  on  the  part  of  man.  The  dog, 
in  other  words,  cannot  relate  itself  in  such  a  clear 
and  perfect  manner  to  the  world  in  which  it  lives  as 
does  the  man,  and  the  human  superiority  arises 
undoubtedly  from  that  higher  evolution  and  develop- 
ment of  his  nervous  apparatus  which  marks  the 
human  estate. 

THE  ESSENTIALS  OF  A  NERVOUS  SYSTEM. — If  we 
compare  the  nervous  system  to  that  of  a  telegraph, 
we  may  find  the  comparison  to  be  thoroughly  justified. 
In  the  construction  of  the  ordinary  telegraph  system 
two  chief  elements  have  to  be  provided.  We  have 
first  to  supply  batteries  or  means  for  developing 
electrical  energy,  and  wires  require  to  be  furnished 
for  the  purpose  of  carrying  or  conducting  the 
electrical  force.  Even  if  wireless  telegraphy  be 
included  in  such  a  comparison,  the  electrical  waves 
will  require  conduction.  The  nervous  system, 
following  out  this  comparison,  complicated  as  it  may 
be,  is  built  up  of  two  elements  which  roughly 
correspond  to  those  of  the  telegraph  apparatus. 
These  two  elements  are  first,  nerve  cells,  and  second, 
nerve  fibres.  It  is  important  to  distinguish  between 
the  functions  of  these  two  elements.  Their  uses  are 
as  clearly  defined  and  distinct  as  are  the  batteries  and 
wires  of  the  telegraph.  Nerve  cells  are  the  origina- 
tors and  receivers  of  the  messages  or  impressions 
through  which  the  nervous  system  is  stimulated  to 
its  work.  A  nerve  fibre  on  the  other  hand,  is  a  mere 
conductor  or  conveyer  of  such  messages.  A  nerve 
has  no  power  of  initiating  any  message  on  its  own 
account.  In  order  that  a  nerve  fibre  may  be  stimulated 
to  carry  a  message,  either  from  brain  to  body  or 


106  HUMAN  PHYSIOLOGY 

from  body  to  brain,  it  requires  the  co-operation  and, 
if  it  may  be  so  termed,  the  supervision  of  nerve 
cells.  This  definition  must  be  kept  fairly  in  mind, 
because  in  common  language  the  term  "  nerve  "  is 
used  as  if  the  bodily  telegraph  wires  represented  the 
most  essential  feature  of  the  nervous  apparatus. 

NERVE  FORCE. — The  particular  form  of  energy 
which  nerve  cells  generate,  and  which  represents 
the  electricity  of  our  bodily  telegraph  system,  is 
termed  nerve  force.  It  is  this  force  which  flows 
along  nerve  fibres,  and  represents  the  messages 
which  stimulate  the  body  to  action  on  the  one  hand, 
and  arouse  the  brain  and  nerve  centres  on  the  other. 
The  rate  at  which  nerve  force  passes  along  nerve 
fibres  has  been  estimated  in  warm-blooded  animals 
at  about  200  feet  per  second.  This  is  a  slow  rate  as 
compared  with  that  of  electricity  or  with  the  speed 
of  light  waves,  which  pass  through  space  at  a  rate 
of  1 86,000  miles  per  second.  The  phrase  "  as  quick  as 
thought"  is  therefore  to  be  accepted  in  a  relative 
sense  only,  though  the  rate  at  which  our  nerve  force 
speeds  along  nerve  fibres  is  quite  sufficient  for  the 
perfect  carrying  out  of  the  work  of  the  nervous 
system. 

NERVE  CELLS  AND  FIBRES. — Nerve  cells  form,  in 
one  sense,  the  central  figure  of  the  nervous  system. 
Like  all  other  cells  a  nerve  cell  is  a  mass  of  living 
protoplasm,  and,  having  regard  to  the  duties  it  dis- 
charges, we  may  safely  conclude  that  the  protoplasm 
of  the  nervous  system  is  of  higher  order  than  that 
represented  in  the  other  cells  of  the  body.  This 
much,  indeed,  we  are  legitimately  entitled  to  assume 
from  the  character  of  the  work  it  performs.  Like 
all  other  cells,  nerve  cells  are  microscopic  in  size, 
some  of  them  extremely  minute.  They  vary  in 


THE  STORY  OF  THE  BRAIN  AND  NERVE      107 

diameter  from  the  1 -500th  or  the  1 -600th  part  of  an 
inch  to  the  1 -5000th  part  of  an  inch,  many  of  the 
cells  in  the  brain  exhibiting  even  more  minute 
dimensions.  The  characteristic  feature  of  a  typical 
nerve  cell  is  that  it  gives  off  branching  threads  or 
processes  of  its  substance  called  dendrons.  Certain 
of  these  connect  the  cell  with  neighbour  cells,  for  as 
a  rule  we  find  in  the  brain  and  spinal  cord  cells  are 
gathered  together  into  groups  to  which  the  general 
name  of  nerve  centres  has  been  applied.  Amongst 
the  processes  or  dendrons  which  a  nerve  cell 
possesses,  one  stands  out  more  prominently  than 
the  rest.  This  process  is  termed  the  axis  cylinder, 
and  differs  from  other  branches  or  dendrons  in  that 
it  can  be  traced  passing  from  the  cell  outwards  to 
the  body.  When  so  traced,  this  axis  cylinder  is 
found  to  become  one  of  the  fibres  of  a  nerve.  In 
other  words,  just  as  the  wires  of  the  telegraph 
system  are  directly  connected  with  the  batteries,  so 
the  nerve  cells  give  off  their  axis  cylinders,  which 
pass  forth  and  become  veritable  wires  of  the  body. 
It  is  unnecessary  to  detail  the  different  forms  and 
shapes  which  nerve  cells  assume,  save  to  record  that 
in  the  spinal  cord  and  elsewhere,  the  cells  give  off 
many  dendrons  or  branches,  and  are  called  multi-polar 
cells,  whereas  those  which  are  characteristically 
typical  of  the  brain  are  triangular  in  shape,  giving  off  a 
branch  at  each  angle,  and  one  from  the  centre  and 
base,  this  last  representing  the  process  which 
ultimately  will  pass  to  become  a  fibre  in  one  of  the 
nerves  of  the  brain.  The  nature  of  the  second 
element  in  the  nervous  system,  the  nerve  fibre,  has 
already  been  sufficiently  indicated.  Even  the  finest 
nerves  of  the  body  are  made  up  of  bundles  of  fibres 
which  originate  from  nerve  cells.  If  these  fibres  be 


108  HUMAN  PHYSIOLOGY 

traced  outwards  into  the  body,  we  discover  that 
their  endings  are  of  diverse  character.  Thus  in  the 
skin  we  find  nerve  endings  devoted  to  the  exercise 
of  the  sense  of  touch.  In  the  nose,  the  ends  of  the 
olfactory  nerves,  or  those  of  smell,  terminate  in 
special  cells  called  olfactory  cells,  which  may  be  pre- 
sumed to  be  the  organs  whereby  the  smell  sense  is 
excited  through  contact  with  odoriferous  particles 
which  come  in  contact  with  them.  More  complex  are 
the  endings  of  the  nerves  of  sight  and  hearing,  these 
being  connected  with  a  complex  apparatus  in  the 
shape  of  eye  and  ear  respectively.  An  important 
point  to  be  noted  is  that  each  ordinary  nerve  of  the 
body,  apart  from  the  nerves  of  sensory  organs  (eye, 
ear,  etc.),  will  be  found  to  include  two  kind  of  fibres 
indistinguishable  from  each  other,  but  performing 
different  duties.  Thus,  as  will  afterwards  be  shown, 
each  nerve  is  like  a  double  telegraph  wire,  in  the 
sense  that  one  set  of  its  fibres  conveys  messages 
from  brain  to  body,  the  other  set  carrying  messages 
in  the  opposite  direction,  from  body  to  brain. 

ABOUT  THOUGHT. — In  the  case  of  the  lowest 
animals  no  question  arises  regarding  the  possession 
of  will,  intellect  or  mind.  They  may  be  considered 
to  be  in  the  position  of  living  machines,  which 
respond  automatically  to  the  impressions  made  by 
the  outer  world  on  their  sensitive  parts.  As,  how- 
ever, we  advance  in  the  animal  scale,  we  begin  to 
find,  with  the  rise  and  development  of  the  nervous 
system,  new  phases  of  nervous  work.  These  fresh 
aspects  are  associated  with  a  higher  development  of 
the  nervous  apparatus,  this  development  mostly 
taking  the  form  of  the  massing  together,  especially 
in  the  head  region,  of  nerve  centres,  which  we  have 
seen  to  represent  collections  of  nerve  cells.  The 


THE  STORY  OF  THE  BRAIN  AND  NERVE      109 

higher  animals  thus  become  raised  from  the  auto- 
matic or  machine-like  life  of  their  lower  kith  and  kin, 
and  develop  accordingly  degrees  of  intelligence  and 
independent  action,  which  vary  with  their  rank ;  this 
advance  attaining  naturally  its  highest  development 
in  man  and  his  neighbour  animals.  In  the  human 
domain  we  meet  a  still  further  development  of  the 
work  of  the  nervous  system.  In  addition  to  the  regu- 
lated play  of  instinct,  a  higher  intelligence  appears 
as  well,  to  which  we  apply  the  terms  reason  and 
consciousness.  It  may  be  said  that  the  highest  level 
of  nervous  work  is  found  in  the  case  of  man, 
because  he  is  conscious  not  merely  of  his  own 
existence,  but  is  also  enabled  to  reason  out  and 
to  understand  generally  the  conditions  under  which 
that  existence  is  passed,  whilst  he  is  also  enabled 
to  adapt  his  life  much  more  readily  than  his 
animal  neighbours  to  the  varying  conditions  of 
life.  Having  regard  to  the  fact  that  nerve  cells, 
or,  in  the  case  under  discussion,  brain  cells,  represent 
the  highest  items  in  man's  bodily  structure,  the 
question  naturally  arises  whether  science  can  lead 
us  to  a  perfect  understanding  of  the  manner  in 
which  these  cells  govern  and  control  existence. 
This  much  is  certain,  at  least,  that  the  living  matter 
of  the  brain  cells  is  the  seat  of  those  particular 
changes  and  actions  arising  from  the  play  of  nerve 
force,  which  can  be  converted  into  force  or  energy 
of  other  kinds.  Thus  a  thought  arising  in,  or 
produced  by,  certain  brain  cells  can  be  converted  at 
once  into  movements  either  simple  or  complex.  The 
act  of  writing  or  of  speaking,  for  example,  involves 
a  whole  series  of  brain  actions,  the  main  feature  of 
which  is  the  conversion  of  thought — which  need  not 
necessarily  manifest  itself  externally  at  all — into  a 


110  HUMAN  PHYSIOLOGY 

variety  of  actions,  having  for  their  object  a  definite 
purpose.  We  thus  arrive  at  the  conclusion  that  the 
brain  cell  is  the  seat  of  those  actions  or  processes 
which  are  generally  spoken  of  under  the  name  of 
"thought"  and  "consciousness,"  and  which  are 
made  manifest  through  the  bodily  actions.  One 
proof  of  this  fact  is  found  in  the  phenomena  of 
disease,  for,  when  certain  cells  undergo  degeneration, 
the  power  of  naturally  exercising  the  brain  becomes 
very  much  altered,  and  the  responsibility  of  the 
individual  may,  as  in  cases  of  insanity,  be  practically 
abolished.  Here,  it  would  seem,  we  stand  on  fairly 
firm  ground  in  assuming  that  the  brain  cell  is  a 
generator  of  that  subtle  and  particular  kind  of  energy 
to  which,  in  one  of  its  manifestations  at  least,  we 
apply  the  name  of  "  thought."  Beyond  this  stage  of 
reasoning  it  is  impossible  to  proceed  with  exactitude. 
What  thought  is  in  its  essence  we  do  not  know.  We 
can  merely  indicate  the  apparatus  by  which  this 
phase  of  mental  action  is  manifested,  namely,  by 
the  highest  protoplasm  or  living  matter  of  which 
brain  cells  are  composed.  As  we  cannot  understand 
the  nature  of  life  itself,  so  we  remain  ignorant  to-day 
of  the  precise  conditions  under  which  the  living 
matter  of  the  brain  cells  gives  rise  to  the  higher 
expressions  of  consciousness. 

How  THE  NERVOUS  SYSTEM  ACTS. — One  general 
principle  is  found  to  underlie  the  working  of  this 
complicated  system.  To  this  principle  the  name  of 
reflex  action  is  given.  A  simple  illustration  of  the 
working  of  the  nervous  system  is  afforded  in  the 
case  of  a  person  withdrawing  the  head  from  a  blow 
aimed  at  him.  Here  the  action  he  performs  begins 
at  the  eye,  which,  like  every  other  organ  of  sense,  is 
a  mere  "gateway  of  knowledge"  devoted  to  the 


THE  STORY  OF  THE  BRAIN  AND  NERVE      111 

purpose  of  affording  information  to  the  brain  through 
a  particular  channel.  The  impression  of  imminent 
danger  is  conveyed  along  the  optic  nerve,  or  that  of 
sight,  arousing  in  other  parts  of  the  brain  conscious- 
ness of  the  attack  about  to  be  made.  The  message 
thus  received  by  certain  brain  centres  is  instantly 
"  reflected  "  to  other  centres,  namely,  those  govern- 
ing the  muscles  of  the  neck,  the  result  being  that 
these  muscles,  stimulated  to  action,  withdraw  the 
head  from  the  threatened  blow.  In  this  case,  the 
incoming,  or  afferent  message  is  "reflected,"  and 
converted  into  an  outgoing  or  efferent  message.  It 
may  be,  however,  that  the  simple  reflex  action  may 
become  more  complicated  and  more  extended  in  its 
range.  For  if  the  threatened  individual  seeks  safety 
in  flight,  the  reflex  action  will  extend  to  the  stimula- 
tion of  the  muscles  of  the  legs  and  body,  carrying 
him  out  of  the  reach  of  danger.  A  man  crossing 
the  street  hears  the  sound  of  a  rapidly  driven  vehicle 
coming  up  behind  him.  In  this  case  the  primary 
message  is  received  by  his  ear,  and  the  same  process 
is  gone  through  as  in  the  case  of  the  eyes.  The 
message  is  "reflected"  from  the  brain  and  sent  to  the 
muscles  by  centres  governing  these  organs  so  as  to 
hasten  the  man's  footsteps,  and  thus  enable  him  to 
seek  safety  on  the  pavement.  When  the  mouth 
waters  at  the  sight  of  something  good  to  eat,  the 
message  conveyed  from  the  brain  is  "  reflected,"  in  this 
case,  to  the  salivary  glands  of  the  mouth,  producing 
a  copious  flow  of  saliva.  Many  more  illustrations 
of  reflex  action  might  be  given,  but  suffice  it  to  say 
that  the  principle  animating  all  our  acts,  whether  of 
simple  or  complex  nature,  is  the  same.  Occasionally 
a  reflex  action  starts  from  the  outside  of  the  body, 
as,  for  example,  when  the  finger  comes  in  contact 


112  HUMAN  PHYSIOLOGY 

with  a  hot  surface  it  is  instantly  withdrawn.  Here 
the  incoming  or  afferent  message  starts  the  action 
which  involves  the  conveyance  of  the  sensation  of 
heat  to  the  centres  governing  the  muscles  of  the 
arms,  which  operate  to  withdraw  the  limb.  For  the 
performance  of  a  reflex  action,  we  therefore  find 
that  what  is  required,  apart  from  more  intricate 
details,  are  essentially  an  incoming  nerve  fibre,  an 
outgoing  nerve  fibre,  and  a  nerve  cell  or  centre 
which  deals  with  and  reflects  the  message  it  receives. 
A  reflex  action  may,  of  course,  be  performed 
unconsciously  and  without  involving  the  arousing  of 
attention.  An  act,  such  as  that  of  closing  the  eye- 
lids in  face  of  danger,  for  example,  takes  place  auto- 
matically, and  is  all  the  more  quickly  performed  on 
that  account. 

THE  SPINAL  CORD. — Confining  our  attention  to  the 
brain  system,  we  find  this  portion  of  the  nervous 
apparatus  (Fig.  30)  to  include  (1)  the  brain  itself 
contained  and  protected  within  the  skull,  (2)  the 
spinal  cord  issuing  from  the  brain  and  representing 
the  main  line  of  the  nervous  system  contained  within 
the  spine,  and  (3)  the  various  nerves  given  off  from 
brain  and  spinal  cord  together.  The  spinal  cord,  it 
should  be  noted,  is  much  more  than  a  great  line  of 
nerve  fibres.  It  contains  both  nerve  cells  and  fibres, 
and  when  we  make  a  section  of  the  cord  we  find 
its  cells  to  be  contained  in  what  is  called  the  grey 
matter  in  the  centre  of  the  cord,  the  white  matter 
outside,  representing  the  nerve  fibres  which  place 
brain  and  body  in  connection.  Thirty-one  pairs  of 
nerves  (Fig.  30)  are  given  off  from  the  spinal  cord. 
One  of  the  most  interesting  discoveries  noted  in 
connection  with  the  nervous  system  was  elicited 
when  the  reason  for  each  spinal  nerve  being 


THE  STORY  OF  THE  BRAIN  AND  NERVE      113 

given  off  by  a  double  root  from  the  spinal  cord 
was  made  plain.  One  root  is  named  the  anterior 
root,  because  it  is  given  off  from  the  front  of  the 
spinal  cord,  the  other,  the  posterior,  proceeding 
from  the  hinder  portion.  Shortly  after  leaving  the 
cord,  the  two  roots  unite  to  form  a  single  spinal 
nerve.  The  hinder  root  of  each  spinal  nerve  may 
be  distinguished  by  the  fact  that  it  possesses  a 
ganglion  or  small  collection  of  nerve  cells.  The 
proper  understanding  of  the  manner  in  which  the 
nervous  system  operates,  and  especially  how  reflex 
action  is  carried  out,  was  made  clear  by  researches 
showing  the  functions  of  these  two  roots.  If  the 
front  root  be  cut  in  an  animal,  whilst  the  hinder  is 
left  intact,  the  animal  loses  the  power  of  movement 
in  the  parts  to  which  the  nerve  is  distributed,  but 
retains  the  power  of  sensation  or  feeling.  If  the 
posterior  or  hinder  root  be  cut,  on  the  other  hand, 
and  the  front  root  left  untouched,  the  opposite 
result  is  seen,  the  animal  retaining  the  power  of 
movement  in  the  parts,  but  losing  the  power  of 
feeling.  From  these  facts  it  is  clear  that  each 
ordinary  nerve  in  the  body  comprises  two  sets  of 
fibres,  those  derived  from  the  front  and  hinder  roots 
respectively-  The  experiment  described  shows  that 
messages  passing  from  the  brain  and  spinal  cord  to 
the  body  pass  out  by  the  front  roots  of  the  spinal 
nerves,  and  are  conveyed  to  the  body  by  the  fibres 
which  represent  the  continuation  of  these  roots. 
On  the  other  hand,  messages  coming  from  the  body 
to  the  brain  and  spinal  cord  pass  along  the  fibres 
of  nerves  belonging  to  the  posterior  or  hinder  root, 
and  then  entering  the  cord,  are  subsequently  dealt 
with  either  by  the  cord  or  by  the  brain,  to  which 
the  messages,  if  need  be,  can  be  conveyed.  The 

H 


114  HUMAN  PHYSIOLOGY 

name  motor  root,  because  its  nerve  fibres  are 
destined  to  convey  messages  resulting  in  movement, 
is  given  to  the  anterior  or  front  root,  whilst  the 
posterior  is  known  as  the  sensory  root,  such  a 
root  being  the  means  for  conveying  impressions 
made  on  the  ends  of  nerves,  and  proceeding 
onwards  to  the  spinal  cord  and  brain.  It  follows 
that  the  nerves  of  sense  belonging  to  eyes,  ears, 
nose,  etc.,  are  "  sensory "  nerves,  because  they 
only  convey  messages  in  one  direction,  from  body 
to  brain  and  cord. 

THE  SPINAL  CORD  AS  A  CENTRE. — Having  regard 
to  the  fact  that  the  spinal  cord  contains  an  abundant 
supply  of  nerve  cells,  we  may  again  remind  ourselves 
that  it  is  much  more  than  a  collection  of  nerve 
fibres,  since  the  possession  of  cells  confers  upon  it 
the  power  of  acting  as  a  nerve  centre,  or  rather  as  a 
series  of  nerve  centres.  There  is  little  doubt  that 
a  large  number  of  actions,  having  reference  to  bodily 
movements  and  other  functions,  can  be  carried  out 
by  the  spinal  cord  independently  of  the  brain,  whilst 
the  cord  may  also  be  regarded  as  acting  in  harmony 
with  the  brain  in  the  performance  of  many  of  the 
acts  which  characterise  our  voluntary  life.  Proof 
that  the  spinal  cord  possesses  a  certain  independent 
action  of  the  brain,  is  afforded  by  an  experiment  in 
which  a  decapitated  frog  has  a  drop  of  vinegar  or 
mustard  placed  on  the  web  of  one  of  its  hind  feet. 
It  will  use  the  other  foot  to  wipe  off  the  offending 
substance,  and  will  execute  a  variety  of  complex 
movements  to  attain  this  end.  Similarly,  in  the  case 
of  a  human  being  who  has  suffered  an  accident 
resulting  in  the  division  of  his  spinal  cord,  and  is 
therefore  unable  to  move  any  part  below  the  break, 
if  the  foot  be  tickled  the  legs  will  be  drawn  up.  In 


THE  STORY  OF  THE  BRAIN  AND  NERVE     115 

frog  and  man  the  independence  of  the  spinal  cord  as 
a  series  of  nerve  centres  is  thus  demonstrated,  for 
in  the  headless  frog  the  control  of  its  movements 
can  only  be  effected  through  the  nerve  cells  of  the 
spinal  cord  which  so  far  govern  its  body  in  the 
absence  of  its  brain,  and  in  man  the  impression  made 
upon  the  feet  passing  up  the  cord  is  dealt  with  by 
the  nerve  cells  below  the  break,  which  thus  "reflect" 
the  message  to  the  muscles,  and  so  produce  the 
movement  of  the  legs.  Research  has  shown  that  in 
the  upper  part  of  the  spinal  cord  there  are  nerve 
centres,  or  groups  of  cells,  which  certainly  exercise 
a  command  over  the  heart  and  other  organs,  the 
working  of  which  is  governed  by  the  sympathetic 
nervous  system.  It  has  already  been  shown  in 
dealing  with  the  heart  how,  for  example,  the  vagus 
nerve  has  the  power  of  slowing  the  heart's  move- 
ments. So  also,  the  regular  movements  of  breathing 
may  be  regarded  as  controlled  from  the  spinal  cord, 
and  in  its  lower  portion  centres  exist  exercising  a 
certain  amount  of  governance  over  the  functions  of 
the  bowel,  bladder,  and  other  organs.  The  spinal 
cord  is  thus  seen  to  be  a  very  effective  deputy  of  the 
brain  itself,  and  the  principle  of  labour  division  in 
the  nervous  system  may  find  an  illustration  in  the 
share  which  the  spinal  cord  assumes  in  the  control 
of  the  bodily  actions,  leaving  the  brain,  so  to  speak, 
free  for  the  discharge  of  more  important  duties. 

THE  EVOLUTION  OF  THE  BRAIN. — It  is  possible  to 
trace  from  the  fish  upwards  to  man,  an  identity  of 
type  or  plan  in  the  build  of  the  brain.  In  fishes, 
frogs,  and  reptiles  the  brain  is  represented  by  a  series 
of  masses  of  nerve  cells  placed,  more  or  less 
distinctly,  in  line.  For  convenience  sake,  we  may 
enumerate  these  masses  as  consisting  of  the  olfactory 


116 


HUMAN  PHYSIOLOGY 


or  smell  parts  in  front,  the  forebrain  coming  next  in 
order,  whilst  there  respectively  succeed  the  middle 
brain  and  the  hind  brain.  As  we  advance  towards 
the  reptiles,  we  discover  that  the  fore  brain  tends  to 
overshadow  by  its  greater  prominence  the  middle 
brain,  and  when  we  arrive  at  the  bird,  we  find  this 


Fig.  31.— THE  BASE  OF  THE  BRAIN 

Showing  the  cerebellum  behind,  and  the  origin 

of  the  spinal  cord.    The  olfactory  lobes  lie  in 

front,  and  the  optic  nerves  behind  them. 

part  with  its  disproportionate  size  arising  from 
increased  growth,  and  also  with  the  enlargement  of 
the  hind  brain,  completely  covers  the  middle  brain. 
In  the  lower  quadrupeds  much  the  same  development 
is  seen.  As  we  advance  a  tendency  is  shown  for 
the  fore  brain  to  increase  in  size,  and  to  grow  not 


THE  STORY  OF  THE  BRAIN  AND  NERVE     117 

merely  forwards,  but  backwards  as  well,  so  as 
to  overlap  the  hind  brain.  This  principle  of  brain 
development  has  its  supreme  exemplification  in 
man.  The  fore  brain  in  man  attains  a  size  far 
exceeding  its  dimensions  in  any  other  animal.  The 
smell  parts,  instead  of  projecting  prominently  in 
front  as  in  fishes,  frogs,  and  reptiles,  are  found  on 
the  under  surface  of  man's  brain  (Fig.  31),  a  feature 


Fig.  32.— SECTION  OF  BRAIN 

Showing  inside  of  left  half  of  cerebrum,  the 

connecting  bridge  of  the  lobes,  cerebellum  in 

section,  and  medulla  at  top  of  spinal  cord. 

also  illustrated  in  many  quadrupeds  as  well.  In 
man,  the  backward  growth  of  the  fore  brain  is  also 
extreme,  and  the  hind  brain  is  completely  covered 
and  hidden  when  the  brain  is  viewed  from  above 
(Pig,  32.)  Such  is  a  brief  account  of  the  evolution 
of  the  brain ;  and  in  the  development  of  man's  brain 
we  are  able  to  trace  with  a  fair  degree  of  accuracy 
the  various  stages  which  represent  the  permanent 
condition  of  the  brain  in  lower  forms  of  life.  The 


118 


HUMAN  PHYSIOLOGY 


-1 


principle  here  represented  is  that  of  the  massing 
together  and  extreme  growth  of  certain  brain 
regions;  that  which  distinguishes  man  being  the 
higher  degree  of  growth  and  development  repre- 
sented, not  merely  in  the  fore  brain  itself,  but 
throughout  the  other  parts  included  in  the 
constitution  of  the  organ  of  mind. 

THE  BUILD  OF  THE  BRAIN. — It  is  perhaps  more 
legitimate  to  speak  of  "  brains  "  than  to  use  the  word 
in  the  singular,  seeing  that  the  brain  is  not  one 

organ,  but  a  complex  array 
of  different  centres.  Thus, 
in  one  part  of  the  brain  we 
may  find  many  different 
centres  to  be  included,  as 
is  the  case  with  the  great 
mass  of  the  brain  (or 
cerebrum)  in  man,  which 
represents  the  principal 
and  most  important  part 
of  the  organ.  The  brain 
regarded  in  a  side  view  as 
it  lies  in  the  head  (Fig.  33) 
would  appear  to  consist  of 
two  large  masses  only.  Of  these,  one  is  much  larger 
than  the  other,  filling  the  greater  part  of  the  cavity 
of  the  skull.  This  is  the  cerebrum,  or  part  to  which 
we  have  hitherto  applied  the  name  fore-brain  (Fig. 
33).  The  second  prominent  portion  of  the  brain  lies 
below  and  behind  the  cerebrum,  and  is  known  as 
the  cerebellum,  or  lesser  brain  (Figs.  31  and  33).  An 
anatomical  examination  of  the  brain  reveals  other 
centres  lying  deeply  imbedded  in  the  base  of  the 
brain,  and  to  these  parts  the  general  name  of  central 
ganglia  has  been  applied.  Regarded  externally  the 


clmi 


Fig.  33— BRAIN  IN  POSITION 

(cb)  Cerebrum. 
(com)  Cerebellum. 


THE  STORY  OF  THE  BRAIN  AND  NERVE     119 

cerebrum  is  seen  to  be  divided  lengthwise  into  two 
halves  or  lobes  (Fig.  32),  the  division  extending  to  a 
short  depth  between  the  lobes,  where  they  are  found 
to  be  connected  together  by  a  bridge  of  nervous 
matter  known  as  the  corpus  callosum.  The  surface 
of  a  man's  brain  is  thrown  into  a  series  of  distinctly 
marked  folds  or  convolutions  (Fig.  34).  These  con- 
volutions are  characteristic  of  many  other  animals, 


PO.F 


Fig.  34.— SIDE  VIEW  OF  BRAIN  REGIONS 

AND  CONVOLUTIONS. 

The  shaded  part  corresponds  to  the  motor  area.    The 

left  lobe  of  the  brain  is  represented  here,  the  front  or 

forehead  region  lying  to  the  left  side. 

but  are  absent  in  the  brains  of  certain  forms,  of  which 
the  beaver,  rabbit,  and  the  like  animals  are  examples. 
The  convolutions  do  not  vary  in  one  individual  from 
those  of  another — that  is  to  say  they  form  a  definite 
pattern,  presenting  occasionally  variations,  but  still 
maintaining  a  close  anatomical  similarity  and  re- 
semblance. For  scientific  and  medical  purposes  the 
convolutions  are  all  duly  marked  and  numbered. 
The  surface  of  the  brain  has  similarly  been  divided 
into  certain  areas  or  regions  corresponding  with  the 


120  HUMAN  PHYSIOLOGY 

bones  of  the  skull.  We  thus  speak  of  the  frontal  or 
forehead  region  of  the  brain  (Fig  34, /.c.),  the  parietal 
or  side  region,  the  temporal  region  at  the  side  of 
the  brow,  and  the  occipital  region  (o.L),  or  that  at 
the  back  of  the  head. 

BRAIN  CELLS. — A  section  of  the  cerebrum  shows 
us  that  its  outer  layer  consists  of  grey  matter  com- 
posed of  brain  cells,  this  grey  matter  following  and 
dipping  into  the  convolutions  thereby  affording  a 
larger  amount  of  cell  material  than  would  be  the  case 
in  a  smooth  brain.  Groups  of  brain  cells  are  found 
in  the  other  parts  of  the  brain.  In  the  cerebrum  the 
grey  matter  is  the  external  layer,  whilst  the  white 
matter,  composed  of  nerve  fibres  which  carry 
messages  to  and  from  the  brain  centres,  forms  the 
inner  portion  of  the  cerebrum.  It  may  be  said  that 
the  most  important  brain  cells  are  those  of  this 
outer  layer  of  the  great  brain.  They  must  exist  in 
millions,  one  estimate  giving  over  800,000,000  as  an 
approximate  number.  The  cerebellum  when  cut  in 
a  section  is  seen  to  have  its  brain  cells  arranged  in 
different  fashion.  Externally  it  presents  a  layered 
appearance  (Fig.  32),  and  in  section  the  white  matter 
forms  a  tree-like  pattern  to  which  the  fanciful  name 
of  arbor  vit<z,  or  "  tree  of  life  "  has  been  given.  The 
white  matter  of  the  brain,  consisting  as  we  have  seen 
of  fibres,  is  arranged  in  definite  bands  or  tracts,  and 
thus,  like  the  telephone  system  of  a  great  factory, 
provides  for  inter -communication  between  the 
various  groups  of  brain  cells,  as  well  as  affording 
communication  between  brain  and  body. 

BRAIN  FUNCTIONS. — The  brain  in  respect  of  the 
functions  it  discharges  might  be  not  inaptly  com- 
pared to  a  three-storied  warehouse.  The  lower 
storey  of  the  warehouse  we  may  suppose  is  given 


THE  STORY  OF  THE  BRAIN  AND  NERVE      121 

over  to  the  carting  and  packing  departments  of  the 
business,  the  men  engaged  representing  the  lowest 
grade  of  employe's.  We  may  suppose  that  the  second 
storey  is  given  over  to  the  routine  business  of  the 
firm  discharged  by  clerks  and  heads  of  departments. 
Above  this,  in  turn,  would  come  the  offices  of  the 
heads  of  the  firm  and  the  partners.  Applying  this 
simile  to  the  brain  itself,  we  find  that  the  chief  lower 
centres  situated  at  the  base  of  the  brain  and  upper 
part  of  the  spinal  cord  are  known  as  the  medulla 
oblongata  (Fig.  32).  If  we  include  the  cerebellum 
(Fig.  33)  along  with  the  medulla  we  may  arrive  at 
some  conception  of  the  resemblance  of  those  parts 
to  the  lower  storey  of  the  warehouse.  The  medulla 
is  a  highly  important  centre  whence  arise  important 
nerves,  among  them  the  vagus  nerve  controlling 
the  heart's  action,  breathing,  and  other  actions. 
We  can  therefore  understand  why  an  animal 
that  is  born  with  the  medulla  developed,  but  the 
rest  of  the  brain  absent,  may  live  for  some  days 
because  its  breathing,  the  heart's  action,  and 
swallowing  may  be  controlled.  The  cerebellum  is 
the  part  of  the  brain  exercising  what  is  called  the 
co-ordination  of  movements,  by  which  term  is  meant 
the  bringing  into  harmonious  action  of  different 
muscular  movements  of  the  body.  The  power  of 
bringing  the  muscles  of  one  side  of  the  body  into 
regulated  action  with  the  muscles  of  the  opposite 
side,  as  in  walking,  in  swimming,  and  in  flying,  is  due 
to  the  control  exercised  upon  them  by  the  cerebellum. 
It  is  to  be  noted  that  the  cerebellum  does  not  confer 
the  power  of  bringing  these  muscles  into  action. 
That  duty  is  accomplished  by  centres  in  the  cere- 
brum specially  devoted  to  their  regulation.  The 
cerebellum  in  this  respect  is  like  the  driver  of  a  coach 


122  HUMAN  PHYSIOLOGY 

who  does  not  give  the  horses  the  power  of  doing 
their  work,  but  controls  their  movements  so  as  to 
impart  a  regular  motion  to  the  vehicle.  It  is  natural 
that  in  disease  of  the  cerebellum  irregularity  of 
muscular  movements  should  be  noted  as  a  prominent 
sympton. 

THE  CENTRAL  GANGLIA. — Buried  deeply  down 
below  the  upper  brain  in  the  centre  of  the  organ  we 
find  certain  masses  of  nerve  cells  constituting  the 
central  ganglia.  The  function  of  these  parts  along 
with  certain  other  and  associated  regions  in  the  brain 
have  not  been  clearly  determined.  The  nearest 
approach  which  can  be  made  to  an  explanation  of 
their  use  is  that  of  assuming  that  they  act  as  deputies 
of  the  upper  brain  and  stand  to  the  latter  structure 
in  the  relation  which  private  secretaries  occupy  to 
their  employer.  One  of  these  central  ganglia  is 
known  as  the  corpus  striatum,  the  other  being  called 
the  optic  thalamus.  It  is  believed  that  the  former  is 
a  kind  of  "brain  clearing  house"  through  which 
motor  messages  are  assorted  and  parcelled  out  when 
proceeding  from  the  cerebrum  to  the  body.  The 
neighbour  mass,  constituting  the  optic  thalamus,  may 
it  is  supposed  act  as  "  a  receiving  house,"  wherein 
messages  from  the  body  passing  to  the  cerebrum  are 
received  and  in  some  fashion  or  other  fitted  for 
appreciation  by  the  cells  of  the  upper  brain  itself. 
It  is  highly  probable  that  the  central  ganglia  may, 
under  certain  conditions,  act  independently  of  the 
cerebrum  itself.  In  persons  who  are  hypnotised  or 
mesmerised,  the  faculties  of  the  cerebrum  may  be 
supposed  to  be  switched  off  for  the  time  being, 
leaving  the  central  ganglia  largely  to  carry  on  the 
parody  of  conscious  life  represented  in  the  mesmeric 
state. 


THE  STORY  OF  THE  BRAIN  AND  NERVE     123 

THE  CEREBRUM. — A  large  amount  of  investigation 
and  research  has  resulted  in  the  mapping  of  the 
cerebrum  into  definite  regions  and  centres.  The 
centres  of  the  cerebrum,  as  revealed  by  science,  are 
not  in  any  sense  to  be  confused  with  those  which 
figure  in  the  old  phrenological  systems  of  localisation 
of  brain  functions.  Phrenology  is  an  effete  mode  of 
explaining  either  the  brain  constitution  or  the  work- 
ing of  the  organ.  The  general  distribution  of  brain 
centres  may  easily  be  remembered  if  we  suppose 
that  each  lobe,  or  half  of  the  cerebrum,  is  divided 
into  three  parts  (Fig.  34).  Of  these,  the  front  third 
may  be  regarded  as  devoted  to  the  higher  operations 
of  mind.  The  cells  of  the  frontal  or  forehead  lobes 
of  the  brain  are  undoubtedly  those  which  may  be 
credited  with  exercising  the  highest  mental  functions 
-represented  by  the  exercise  of  our  consciousness  and 
will.  This  section  may  therefore  be  termed  the 
intellectual  area  of  the  brain.  The  middle  third  we 
may  term  the  motor  area,  since  the  centres  repre- 
sented in  the  arrangement  of  brain  cells  in  this 
region  are  devoted  to  the  government  and  control  of 
the  muscles  of  the  body.  The  hinder  third  of  each 
half  of  the  cerebrum  may  be  termed  the  sensory  area. 
Here  we  find  the  centres  specially  connected  with 
the  receiving  of  impressions  from  eyes,  ears,  and 
other  organs  of  sense,  and  it  is  probably  in  these 
centres,  also,  that  such  messages  are  fitted  for 
transmission  to  the  intellectual  centres,  there  to 
have  their  meaning  translated  and  appreciated  by 
our  consciousness. 

THE  DOUBLE  BRAIN. — The  two  halves  of  the 
cerebrum,  right  and  left,  govern  each  the  opposite 
side  of  the  body,  although  in  a  limited  degree  each  half 
also  exercises  a  certain  amount  of  control  over  its 


124  HUMAN  PHYSIOLOGY 

own  side.  The  nerve  fibres  of  each  half  of  the  brain 
cross  in  the  upper  part  of  the  spinal  cord  to  the  op- 
posite side  of  the  body,  and  so  give  us  right-handed- 
ness associated  with  the  left  lobe  of  the  brain,  as 
the  right  side  of  the  brain  in  turn  controls  the  left 
side  of  the  body.  The  left  side  of  the  brain  is  thus 
figured  forth  as  the  superior  half  or  lobe,  seeing 
that  its  functions  are  more  complex  and  involve  the 
discharge  of  more  important  duties  (the  conduct  of 
the  right  hand,  for  example)  than  those  performed 
by  its  neighbour,  the  right  half.  To  what  this 
superiority  and  selection  of  the  left  half  of  the 
brain  as  the  controlling  lobe  is  due,  is  difficult  to 
determine.  Whether  this  superiority  arose  from  the 
body  acting  on  the  brain,  or  whether  right-handed- 
ness was  developed  through  the  left  half  of  the  brain 
acquiring  a  dominant  power  over  the  right  half,  it  is 
impossible  to  say.  One  important  fact,  however, 
teaches  us  the  superiority  of  the  left  half  of  the  brain 
in  an  unexampled  manner.  This  fact  is  found  in  the 
demonstration  that  the  speech  centre  of  the  left  side 
of  the  brain  is  that  by  which  the  ordinary  right- 
handed  mortal  exercises  this  special  human  gift.  A 
similar  speech  centre  exists  on  the  right  side,  for  the 
centres  of  the  brain  are  in  duplicate ;  but  the  right 
centre  §eems  to  remain  in  abeyance,  and  it  is  prob- 
ably only  in  the  case  of  left-handed  persons,  whom 
the  right  lobe  dominates,  that  speech  is  controlled 
from  the  brain's  right  side.  In  cases  of  the  disease 
known  as  aphasia,  in  which  the  power  of  speech  is 
lost,  while  that  of  the  other  faculties  may  remain 
practically  unimpaired,  the  left  speech  centre  is 
found  to  be  affected.  In  cases  where  this  centre 
has  been  destroyed  and  where  a  certain  amount  of 
recovery  of  speech  has  taken  place,  it  is  believed 


THE  STORY  OF  THE  BRAIN  AND  NERVE      125 

that  the  right  speech  centre,  hitherto  dormant,  has 
come  into  play. 

THE  SENSES.— The  senses  are  estimated  to  be  five 
in  number,  including,  sight  (Fig.  35),  hearing  (Fig. 
36),  touch,  taste,  and  smell.  It  is,  however,  most 
probable  that  we  possess  a  sense  of  weight,  and  also 
that  of  temperature  or  heat.  Some  authorities  incline 
to  believe  in  the  existence  of  other  senses,  amongst 


f  Coptic  nerus 
posterior  chamber. 


Fig.  35.— SECTION  SHOWING  STRUCTURE  OF  THE  EYE. 

them  a  sense  of  direction  still  imperfectly  developed 
in  man.  The  senses  are  mere  "gateways  of  know- 
ledge"— in  other  words,  they  simply  receive  inform- 
ation from  the  outer  world,  modify  it,  and  transmit 
to  the  corresponding  centres  in  the  brain, 
which  in  turn  pass  forward  the  information  to  be 
submitted  for  judgment  by  the  intellectual  centres. 
Thus  we  do  not  really  see  with  the  eye  or  hear  with 
the  ear.  Seeing  and  hearing  represent  intellectual 
acts  to  which  the  work  of  the  eye  and  ear  is  only  a 


126 


HUMAN  PHYSIOLOGY 


necessary  preliminary.  The  work  of  the  senses  is 
too  complicated  for  treatment  in  the  present  instance. 
It  is  a  topic,  however,  of  vast  interest,  and  will  well 
repay  investigation  by  the  aid  of  manuals  specially 
devoted  to  the  exposition  of  the  subject. 


Fig.  36.— SECTION  THROUGH  THE  EXTERNAL  MEATUS, 
MIDDLE  EAR,  AND  EUSTACHIAN  TUBE. 

(a)  External  auditory  passage ;  (&)  attic  of  tympanum  ; 

(c)  Eustachian  tube  ;  (d)  internal  auditory  meatus  ; 

(e)  cochlea  ;   (/)  ossicles  ;  (g)  membrana  tympani, 

or  "  drum  "  ;  (h)  styloid  process. 


THE    END. 


INDEX 


PAGE 

PAGE 

Absorption  

...     52 

Deglutition  (see  Swallowing) 

Air      

78 

Diets  

22,  24 

„  Cells 

..      88 

Diet  Experiments  ... 

...    25 

,,  Impure     .. 

..      82 

Digestion      30 

et  seq. 

Amylopsin     .. 
Aphasia 

..      51 
..    124 

„         in  Stomach 
Digestive  Glands    ... 

...    44 
...     32 

Arteries 

..      58 

„         System  ... 

...     30 

Eggs  

22 

Balance  Sheet  of  Body 
Bile    

...    97 
50 

Elements      
Energy  Foods 
Epiglottis     

...     11 
...     20 
...     40 

Blood            

..      61 

Bloodvessels 

..      58 

Brain  Cells  ... 

..    120 

,,      Evolution  of 
,,      Functions  of 
,,      Structure  of  ... 
Breathing     

..    115 
..    120 
..    118 
..      89 

Fibres           
Foods           
„     and  Work    ... 
„     Classification  of 

...       6 
...     13 

...     28 
...     16 

„     Need  for 

...     14 

„     Uses  of 

...     21 

Capillaries    

...     59 

Cells  

6 

Gastric  Juice 

...     42 

„     Work  of 

8 

Glycogen      

...     49 

Central  Ganglia 

..    122 

Cerebrum      

..    123 

Cerebellum  

118   121 

Chemistry  of  Body 

..      11 

Heat,  Bodily 

.      92 

Chyle  

53 

Heart            

66 

Cilia    

87 

„     Beats  of 

72 

Circulation  of  Blood    56  et  seq. 

Regulation  of 

.      74 

Compounds  

...     12 

„     Work  of        ... 

.      73 

Corpuscles  of  Blood 

62,  63 

Human  Characters 

.  3,4 

127 


128 


INDEX 


PAGE 

PAGE 

Inflammation         65 

Saliva           

35,  36 

Senses          

...  125 

Skin    

90 

„    Action  of 

..      92 

Kidneys        94  et  seq. 

„    Care  of 

..      93 

„    Glands  

..      91 

Speech  Centres 

..    124 

Spinal  Cord 

..    112 

Liebig's  Views       25 

Spleen 

..      54 

Liver  and  its  work...  46  et  seq. 
Lungs           77  et  seq. 
Lymphatics  53 

Steapsin 
Stomach 
Swallowing 
Sweetbread 

..      51 
..      40 
..      39 
..      50 

Sympathetic  System 

..    101 

Man's  place  in  Nature     ...      2 

Milk    22 

Minerals       19 

Teeth  

37 

„     Structure  of  ... 

...     39 

Thoracic  Diet 

...     53 

Nerve  Cells  105 
„      Fibres          105 

Thought       
,Trypsin         

...  108 
...    51 

„      Force  105 

Nervous  System         101  et  seq. 

„            „       Action  of 

103,  110 

Urine  .~ 

...    96 

Ovum  6 

Valves  of  Heart     ... 
Veins  

"•il 

Pancreas  (see  Sweetbread) 
Peptones      45 

Ventilation  81 
Vertebrates,  Plan  of 

et  seq. 
...      2 

Physiology  Defined          ...      1 
Ptyalin          36 

Water  

18 

Reflex  Action         110 

Windpipe      

...     84 

Rennin         51 

Work  of  Body 

98,99 

HILNBR  AND  COMPANY,   LIMITED,   PRINTERS,   HALIFAX. 


-wm 

,N  i  \  r.  K>  1  I   ' 


280862 


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